New Generator Set Installation and Compartment Fabrication
Written by RV Systems Lead, RV Systems and Electrical Lead, OCRV Center. Reviewed by Structural Repair Lead
In shortFitting a set is mostly compartment fabrication, exhaust routing and chassis weight, not electrical work. Installations run $2,500 to $12,000+ across 12 to 45 hours.
What does installing a new RV generator set involve?
A generator installation means building or adapting a compartment, mounting the set on isolators, routing exhaust safely away from windows and doors, adding a fuel pickup, and integrating with the transfer switch. Rancho Santa Margarita owners have these built in Yorba Linda because the work is fabrication as much as it is wiring.
- Exhaust must terminate well clear of windows, doors and intakes
- Fuel pickup tubes are set so the set cannot empty the chassis tank
- Compartment weight changes axle loading and has to be checked
- The set feeds the coach through a transfer switch, never a plug
- Price range
- $2,500 to $12,000+12 to 45 labor hours at $260 per hour
- Labor rate
- $260 per hourMechanical and electrical department
- Typical turnaround
- 5 to 15 shop daysFabrication and cure times are scheduled rather than compressed
- Written estimate
- $150Credited in full against an authorized repair
- Fuels handled
- Gasoline, diesel and LP vaporChosen to match what the coach already carries
Last verified
Adding a set to a coach that never had one is a construction project with an electrical component, not the other way around. The generator itself arrives on a pallet and bolts down in an afternoon. What takes the fortnight is building somewhere for it to live, getting exhaust out of the coach safely, and feeding it fuel without compromising the chassis supply.
Replacing a set that has reached the end is usually simpler, but only usually. Compartment dimensions change between model generations, mounting patterns shift, and a modern unit frequently wants different ventilation than the one it is following. We measure before we quote rather than assuming a drop in fit.
Why owners add a set to a coach that never had one
The usual trigger is load growth. A trailer bought with a single roof air and an absorption refrigerator gets a residential refrigerator during a remodel, then a second air conditioner, then induction cooking, and the electrical plan quietly falls a long way behind the appliance list. Battery and solar can carry a lot of that, but neither will start a compressor at four in the afternoon in August without a very large investment.
The second trigger is commercial. Food trucks, workshops, clinics and command units need power that does not depend on where they parked, and their duty cycle makes a generator the practical answer rather than an optional convenience. Those installations are specified around continuous output rather than around occasional camping use, which changes both the model and the compartment.
- Appliance additions that outgrew the original electrical plan
- A failed original set with no remaining parts support
- Commercial duty cycles that need output regardless of location
- Conversions where the build specification changed after the body was finished
Choosing a fuel and sizing the set to the loads
Fuel choice usually follows what the coach already carries. A gasoline motorhome takes a gasoline set drawing from the chassis tank through a dedicated pickup. A diesel pusher takes a diesel set. Towables have no engine fuel supply at all, which is why LP vapor sets are common on fifth wheels and trailers where the propane system is already there and sized to support the draw.
Sizing is arithmetic rather than opinion. We add up the loads that must run simultaneously, allow for the surge a compressor demands at start, and choose a rating with genuine headroom above that figure. Undersizing produces a set that nuisance trips and lives at full output, which is hard on it. Oversizing produces the light loading problem that fouls a set from the other direction.
| Coach type | Usual fuel | Supply arrangement |
|---|---|---|
| Gasoline motorhome | Gasoline | Dedicated pickup in the chassis tank |
| Diesel pusher | Diesel | Dedicated pickup, returns plumbed separately |
| Fifth wheel or trailer | LP vapor | Tied into the propane system with regulator capacity checked |
| Commercial conversion | Diesel or LP | Chosen around duty cycle and refuelling logistics |
The compartment is most of the job
A generator compartment has to do four things at once. It carries a heavy mass that vibrates continuously, so the structure beneath it must be rated for that rather than borrowed from a storage floor. It seals against the living space so exhaust and fumes cannot migrate inward. It breathes enough to keep the set within its temperature limits in an Orange County August. And it opens well enough that the set can actually be serviced afterward.
Getting those four to coexist in an existing coach is where the hours go. Frame members are where they are, tanks are where they are, and the openings on that side of the body were placed by somebody who never imagined a generator would live there. On larger installations a slide out tray solves the service access problem elegantly, and it adds its own structural demands in exchange.
Before you proceed
Combustion air must come from outside the coach, never from the living space. A compartment that is not properly sealed and separately ventilated turns a generator into an appliance that competes with the people inside for oxygen.
Exhaust routing and carbon monoxide
This is the part of the project where mistakes hurt people rather than equipment. Exhaust has to leave the coach at a point well clear of every window, door, roof vent and fresh air intake, and it has to keep doing so when the coach is parked at an angle or when a breeze pushes fumes back along the body. Terminating at the nearest convenient hole in the skin is not an installation, it is a hazard.
Routing matters as much as termination. Tubing is kept away from fuel lines and wiring, supported so it cannot resonate against the frame, and isolated at the connection so engine movement is not transmitted into the body. We also verify carbon monoxide detection inside the coach as part of commissioning, because a detector that has aged out is not protection.
- Terminate well clear of every window, door, vent and intake
- Route away from fuel lines and electrical runs
- Support the tubing so vibration cannot resonate through the body
- Confirm working carbon monoxide detection before handover
Tying a new set into the coach electrical system
The set never plugs into the coach. It feeds an automatic transfer switch installed ahead of the load center, and that switch decides which source the panel sees. Doing it any other way puts the responsibility for source selection on whoever is holding the cord, and it permits configurations that should not be physically possible.
Beyond the switch, the feed is sized and protected to the set output, remote start goes to a panel the owner can actually reach, and any energy management or surge equipment already fitted is reviewed so it sits in the right position in the chain. On coaches where an inverter charger is already installed, the interaction between it and the new source is checked during commissioning rather than discovered on the road.
Where the twelve to forty five hours go
Installations bill at $260 per hour from the mechanical and electrical department, and the spread across this page is a fabrication spread rather than an electrical one. Dropping a replacement set into a compartment that is already sound, already ventilated and already wired occupies the bottom of the range. Building a compartment into a fifth wheel that never had one, with a new fuel path and a transfer switch, occupies the top.
The set itself, isolators, exhaust components and the transfer switch carry standard parts markup, with tax on parts and materials. Fluid and LP handling brings the $45 hazmat charge. A written repair estimate is $150 and credits in full. Projects at this scale pass both deposit thresholds, so a deposit applies at authorization and a further amount when parts arrive.
On cost
We quote the compartment separately from the set on every installation. Owners are entitled to see how much of the number is hardware and how much is building somewhere for that hardware to live.
Weight, axle load and what the chassis allows
A generator plus its compartment, exhaust and fuel provision is a meaningful mass added at a specific point on a chassis that already has a rating. On a large motorhome the margin usually exists. On a lighter travel trailer, adding a set on one side without accounting for it can push an axle past its limit or introduce a lateral imbalance that shows up as tire wear and handling complaints.
So the weight conversation happens before the model is chosen rather than after the compartment is built. We check axle ratings, look at what is already loaded on that side, and where necessary steer an owner toward a lighter set or a different location. It is a less exciting conversation than output ratings and it prevents a genuinely expensive mistake.
What is included
- Site survey and compartment planning
- We establish where the set can live given frame members, tank positions, holding tanks, wiring runs and the openings on that side of the coach.
- Compartment fabrication or rebuild
- Floors, walls and doors are built or repaired to carry the weight, seal from the living space and take the ventilation the set requires.
- Mounting on isolators with proper support
- The set is carried on structure rated for it, not on a floor panel, and isolators are matched to the mass so vibration is not transmitted into the body.
- Exhaust routing and termination
- Tubing is routed away from fuel lines and wiring, hung so it cannot resonate, and terminated well clear of every opening on the coach.
- Fuel supply with a dedicated pickup
- Gasoline and diesel installations receive a pickup that cannot empty the chassis tank, and LP installations are pressure tested at the regulator.
- Transfer switch integration and remote startwhere applicable
- The set feeds the load center through an automatic transfer switch, with the remote panel wired to a location the owner can reach.
How the work runs
Survey the coach and choose a location
2 to 4 hours
Frame members, tanks, wiring runs, holding tank positions and body openings all constrain where a set can go. We map those first and present the realistic options with their trade offs rather than starting work and discovering a conflict.
Confirm weight, fuel and sizing
1 to 2 hours
The set is sized to the loads it must carry, matched to a fuel the coach already stores where possible, and its mass is checked against axle capacity. On towables this step regularly changes the model selected.
Build the compartment
6 to 20 hours
Structure goes in to carry the load, the enclosure is sealed from the living space, intake and discharge openings are cut to specification, and a serviceable door is fitted. This is the largest single block of hours in the project.
Mount, plumb and route exhaust
3 to 12 hours
The set lands on isolators, the fuel path is built with a dedicated pickup or an LP connection that has been pressure tested, and exhaust is routed and terminated clear of openings with hangers that isolate vibration.
Wire in, commission and load test
3 to 10 hours
An automatic transfer switch goes in ahead of the load center, remote start is wired to an accessible panel, and the set runs against a full coach load while voltage, frequency and compartment temperature are logged.
What this costs
$2,500 to $12,000+
12 to 45 labor hours at $260 per hour, mechanical and electrical.
- Hazmat and disposal $45 flat when chemicals, refrigerant or LP is involved.
- Parts at $100 or less carry 100 percent markup. Parts over $100 carry 35 percent. Special order parts require a full non refundable deposit at order.
- Sales tax of 7.75 percent applies to parts and materials. Labor is not taxed.
- A 50 percent deposit is taken at authorization on any job over $2,000, with an additional 25 percent when parts arrive on any job over $10,000. Final balance is due at pickup.
- Replacing a set into an existing sound compartment sits at the bottom of this range.
- A first time installation into a towable with a fabricated compartment and new fuel path sits at the top.
- The set itself, the transfer switch, isolators and exhaust components are billed as parts with standard markup.
How estimating is billed
- Written repair estimate: $150, credited in full against an authorized repair.
- In depth diagnostic, scan and programming: $285 per hour, one hour minimum, credited in full against an authorized repair.
- In shop pre purchase inspection: $400 to $1,200 depending on unit size and systems count.
- Insurance walk ins are accepted during posted hours. All inspection and estimating work is performed in shop at the Yorba Linda facility.
What you will notice first
- A fifth wheel or trailer with no onboard power source and a growing appliance list
- An existing set that has failed and is no longer supported with parts
- A coach that trips its inverter every time roof air is needed away from hookups
- Compartment corrosion or floor rot beneath a set that has been leaking fluids
- A mobile business that has outgrown the output of its original unit
- An older set producing an exhaust note and smell inside the living space
- A conversion build with the electrical load planned but no generation to match
- A rental unit returning from bookings with repeated shore power dependency complaints
How this fails, and what we do about it
| Failure mode | How we diagnose it | The fix |
|---|---|---|
| Exhaust terminating too close to an opening | Exhaust smell inside the coach with the set running and a window or roof vent open, or a carbon monoxide alarm sounding during generator use. Measuring the distance from the tailpipe outlet to the nearest opening usually shows why immediately. | Reroute and extend the exhaust so it terminates well clear of every window, door, roof vent and fresh air intake, with hangers that isolate vibration from the body. |
| Compartment that cannot breathe | A newly installed set running hot, derating or shutting down on temperature, with intake and discharge openings smaller than the manufacturer specified. Common when a set is fitted into a bay that was designed for storage. | Enlarge or add openings, separate intake from discharge so hot air is not recirculated, and line the compartment so combustion air is drawn from outside rather than from the coach. |
| Fuel pickup set too low in the tank | The generator runs the chassis tank dry, or a coach that had plenty of fuel arrives at the pump on fumes after a night of generator use. Inspecting the pickup shows a tube that reaches near the bottom of the tank. | Fit a dedicated pickup tube that stops well above the chassis engine pickup, so the set stops before it strands the coach. This is standard practice on factory installations and frequently missing on aftermarket ones. |
| Set connected without proper source switching | A cord and plug arrangement where the owner unplugs from shore and plugs into the generator by hand. Beyond being inconvenient, it allows two sources to be connected in configurations that should never occur. | Install an automatic transfer switch ahead of the load center so the coach cannot see both sources at once, and wire the set to it on a properly sized and protected feed. |
Why it happened
- Original equipment sets that reached end of parts support, where the economical path is a current model rather than a search for obsolete components
- Load growth over the life of a coach, as owners add a residential refrigerator, a second roof air or induction cooking that the original set was never sized for
- Corrosion or rot in a compartment floor beneath a set that leaked oil or fuel over several seasons, which has to be rebuilt before anything new goes in
- Towable units bought without a generator provision, where the whole compartment, fuel path and electrical tie in has to be created from scratch
- Commercial conversions where the specification changed after the body was built, leaving the power plan behind the equipment plan
- Exhaust systems on older installations that terminate too close to a window or door and cannot be brought into a safe configuration without relocation
Parts and brands we work with
- Cummins Onan RV QG gasoline sets and RV QG LP models for towables
- Cummins Onan QD diesel sets for pusher chassis and diesel fueled coaches
- Slide out generator trays with service pullouts on larger installations
- Vibration isolator mounts sized to the set and the mounting structure
- Iota, Parallax and Southwire automatic transfer switches for the tie in
- Marine grade exhaust tubing, hangers and stainless termination fittings
What not to try yourself
- Mounting a set on a storage bay floor panel. That structure was designed to carry folding chairs, and the vibration path into the body will crack cabinetry and open sealed seams.
- Running exhaust to the nearest convenient exit point. Carbon monoxide entering through a window, a roof vent or a fresh air intake is the one failure on this page that harms people rather than equipment.
- Plumbing a generator pickup to the bottom of the chassis tank. A set that empties the tank overnight leaves a coach unable to move under its own power.
- Feeding the coach from a set through a cord and a plug. Source switching belongs in an automatic transfer switch where the coach physically cannot see both supplies at once.
Which vehicles we do this on
Vehicles we perform Generator Installation on
StandardStandard fifth wheel repair concentrates on the pin box and upper deck welds, the floor at the step up transition, the front cap above the pin and the roof front radius seamToy HaulerToy hauler fifth wheel repair concentrates on the ramp door hinge line at the rear wall, garage floor deflection between crossmembers, and sag in the frame cantilevered behind the axlesTravel TrailerTravel trailer repair covers A frame tongue welds, the front cap that takes road debris, the roof front radius seam, sidewall delamination starting at a window corner, and equalizer and axle wearCamper Van ConversionCamper van conversion repair covers aftermarket build outs in bare cargo vans: Sprinter, Transit and ProMaster shells finished by a shop or an ownerFood TruckFood truck repair covers the step van body, the serving window aperture and its header, the roof hood curb, the coved floor under the cooking line and the generator compartmentMobile WorkshopMobile workshop repair covers bench and vise mounts, compressor and generator deck plates, roll up door tracks that bind after a body racks, and shelving anchors in thin sidewall postsPeople ask why an install takes two weeks when the generator bolts down in an hour. I show them the compartment. On a fifth wheel with no provision we are building a box that carries two hundred pounds of vibrating machinery, seals against the living space, breathes enough air to keep the set cool in August, and drops out for service. Then the exhaust has to leave the coach somewhere that will never put fumes near a window. The generator is the easy part of a generator installation.
Appendix: questions and answers
- Can a generator be added to a travel trailer that never had one?
- Yes, and it is the largest version of this job. A compartment has to be built with structure to carry the set, sealing against the interior, ventilation and service access, plus an LP or fuel supply and a transfer switch. Weight and axle capacity get checked before a model is chosen.
- Should a fifth wheel run an LP generator or a gasoline one?
- LP vapor is the common answer because a towable carries no engine fuel supply, and the propane system is already aboard. What matters is regulator and tank capacity, since a set adds a substantial draw. We verify that the existing propane system can support the load before specifying one.
- Why does a generator installation take two weeks when the unit bolts down quickly?
- Because the set is the small part. Building a compartment that carries the mass, seals from the living space, breathes enough to stay cool and still opens for service is the bulk of the labor, and exhaust routing has to be done carefully rather than quickly.
- How far does generator exhaust need to be from a window?
- Well clear of every window, door, roof vent and fresh air intake, with the coach parked at an angle taken into account. This is the one item on an installation where an error harms people rather than equipment, so we route and terminate conservatively and verify detection before handover.
- Will an onboard generator drain my fuel tank completely?
- Not when the pickup is installed correctly. A dedicated tube stops well above the chassis engine pickup so the set shuts down while the coach can still be driven. Aftermarket installations that plumb to the bottom of the tank are the reason this question gets asked.
- How much generator capacity should I specify above my actual load?
- Enough to cover compressor surge with genuine headroom, but not so much that the set spends its life lightly loaded. Undersizing causes nuisance tripping and constant full output running. Oversizing causes carbon fouling. We total the simultaneous loads and size deliberately between those two failure modes.
Open a file on this repair
Tell us the vehicle, what happened and whether a claim is open. We will tell you what the scope looks like and what it takes to get you back on the road.
Or call (949) 799-3387