--- title: "Why an RV Slide Seal Leaks After Months in Storage" description: "A bulb seal left compressed for seven months took a permanent set and stopped sealing. What compression set is, and how to store a slide room so it lasts." focus_keyword: "why an rv slide seal leaks after months in storage" canonical: https://ocrv.me/blog/a-bulb-seal-that-set-flat-in-storage/ kind: blogPost updated: 2026-07-29 source: OCRV Center --- # A Bulb Seal That Set Flat Over a Storage Season > Rubber left under load for months stops springing back. This seal recovered to **a third of its free height**, which is why the room leaked at the first rain and **not before storage**. ## Why does an RV slide seal start leaking after a long storage period? Because a bulb seal held compressed for months takes a permanent set and no longer expands to fill its gap. Rancho Santa Margarita owners who store a unit with the room extended often find the leak at the first rain, and by then the seal has to be replaced rather than conditioned. - Compression set is permanent, not a temporary flat spot - Store the room retracted so bulb seals sit unloaded - Cycle the room monthly if it has to sit extended - A conditioned seal resists set, a cracked one is already finished ### Key facts | Item | Value | | --- | --- | | Storage period | 7 months, room extended | | Bulb free height | About 1.25 inches when new | | Recovered height measured | Roughly one third of free height | | Mechanical and electrical labor | $260 per hour | | Recommended cycling interval | Monthly while in storage | The unit had spent seven months in a storage lot with the largest room extended, because the owner had been using it as a weekend cabin on the lot itself and it was easier to leave it out. The first real rain of the season put water on the interior floor along the front edge of that room, and nothing about the mechanism had changed. What changed was the rubber. A bulb seal is a hollow rubber extrusion that works by being squeezed and pushing back. Squeeze it for a week and it recovers. Squeeze it for seven months in Southern California sun and a meaningful part of that recovery is simply gone. This is a maintenance and storage story rather than a repair story, and it is the most avoidable water intrusion we see. ## Two different seals doing two different jobs A slide room has a bulb seal and a wiper seal and owners routinely mix them up. The bulb is the fat hollow extrusion that gets crushed between the room's flange and the sidewall when the room is fully in or fully out. It is a static seal and it works by compression. The wiper is the thin flexible blade that lies against the moving room surface, and it works by contact pressure as the room travels. They fail differently and they should be inspected differently. A wiper fails by wearing thin, tearing at a corner or being folded the wrong way by a room that came in crooked. A bulb fails by cracking from ultraviolet exposure or by taking a compression set. The room that leaks only when it is extended has a bulb problem at the outer position. The room that leaks in both positions usually has a wiper or a geometry problem. - Bulb seal: hollow, static, works by being compressed - Wiper seal: thin blade, dynamic, works by contact on the moving room - Leaks only in one room position point at the bulb for that position - Leaks in both positions point at the wiper or at room geometry ## What compression set actually is EPDM and similar seal rubbers are elastic within limits. Hold one at a fixed deflection and the polymer chains slowly rearrange to accommodate the new shape. Release the load and the material recovers most of the way, then keeps creeping back for a while, and then stops short of where it started. That shortfall is compression set and it is permanent. Time, temperature and deflection all make it worse, and a storage lot in Orange County supplies plenty of the second. Roof surfaces and the top of a slide flange get hot enough on an August afternoon that the rubber sitting under load there is well above the temperature at which set accumulates quickly. Seven months is not an unusual storage period and it is more than enough. ## How to check a bulb seal in five minutes Retract the room fully, then look at the bulb along its whole length while it is unloaded. A healthy bulb is round in cross section and springs back when you press it with a thumb and let go. A set bulb is oval or flat on one face, does not spring, and often shows a bright line along the crease where the surface has been stretched. Then compare. Almost every unit has a section of the same seal profile somewhere that has spent less time under load, usually at the very ends of the run or on a small room that gets used less. Press a known good section and press the suspect section and the difference is obvious by hand. You are not looking for a number, you are looking for whether it pushes back. ## Room in or room out for storage Retracted, in almost every case. With the room in, the outer bulb seal sits unloaded and the wiper seals rest against the room surface without the sustained squeeze they see at the extended position. The unit also presents less surface to wind, less shade for rodents and a smaller footprint in a lot where you may be paying by the foot. There is one honest exception, which is a unit whose interior would be damaged by having furniture pressed against a slide face for months, and a small number of floor plans where the room in position blocks a roof vent. If you must store extended, cycle the room once a month. Ten minutes of movement redistributes the load on the rubber and it is the single highest value habit in this whole article. > **warning:** Do not spray a general purpose lubricant on a bulb or wiper seal. Petroleum based products swell and soften EPDM. Use a product intended for rubber, applied to the seal only, and keep it off the rails entirely. ## Conditioning that actually helps Twice a year, wipe the seals down with clean water and a soft cloth, let them dry, then apply a silicone free rubber conditioner made for automotive or RV seals. That treatment does not reverse set and nobody should sell it as though it does. What it does is keep the surface flexible and slow ultraviolet degradation, which delays the cracking failure that usually finishes a seal before set does. Timing matters more than product choice. Do it before the unit goes into storage and again when it comes out, because the storage period is when the rubber is under load and getting no attention. A conditioner applied to a seal that already has a crease and a bright stretch line is being applied too late, and we will tell you that rather than take the labor. ## What this one needed New bulb seal on the front and top edges of the affected room, roughly twenty two feet of extrusion, plus a wiper replacement on the leading edge where it had been folded during one retraction. The old bulb came out of its retention channel with a plastic pick and the channel was cleaned before the new extrusion went in, because forty years of experience says a channel with debris in it holds a seal at the wrong depth. Interior work was limited to lifting and drying the floor covering along the room edge, which had been wet for less than a week. That is the difference between finding this at the first rain and finding it in March. A subfloor that has been wet for a season is a completely different job and it is the reason we push the storage habit rather than the seal replacement. ## Questions and answers ### Can a bulb seal that has taken a set be brought back? No. Compression set is a permanent rearrangement of the polymer, not a temporary flat spot. Conditioners keep a seal flexible and slow ultraviolet damage, which is worth doing, but nothing restores lost free height. Once a bulb no longer springs back under thumb pressure it needs replacing. ### Should a slide room be stored extended or retracted? Retracted for almost every unit. That leaves the outer bulb unloaded, reduces wind exposure and shrinks the footprint in a paid lot. If a floor plan forces you to store it extended, cycle the room fully in and out once a month so the rubber is not held at one deflection for the whole season. ### How do I tell a bulb seal from a wiper seal? The bulb is the fat hollow extrusion that gets crushed when the room reaches a fully in or fully out position. The wiper is the thin blade that lies against the moving room face and sweeps it during travel. They fail differently, so knowing which one is leaking changes what gets ordered. ### What does it mean if a slide leaks only when extended? It points at the bulb seal that compresses at the extended position rather than at the wiper. A room that leaks in both positions is more likely a wiper problem or a geometry problem, where the room is sitting out of square and the seal is not making contact along its full length. ### Why clean the retention channel when replacing a seal? Because grit and old adhesive in the channel hold the new extrusion at the wrong depth, which reduces effective compression along that section. Five minutes with a plastic pick and a vacuum sets the new seal at its designed height, and skipping it produces a seal that leaks in exactly the same place. --- Source: [OCRV Center](https://ocrv.me/blog/a-bulb-seal-that-set-flat-in-storage/). Last verified 2026-07-29.