A fiberglass roof is the one RV roof I don't worry about as a membrane — because there isn't one. It's a rigid fiberglass panel finished with gel coat, the same resin finish you see on a boat hull. No rubber to replace, very few seams, and it will outlast the rig if you take care of it. Ignore it, and the sun eats the finish first.
Most fiberglass roof calls I get are not panel leaks. They're chalky white streaks down the sidewalls, a dull roof that never comes clean, and fine cracks around a skylight or the front cap radius. All three start in the gel coat.
Read the gel coat first
Gel coat is a thin, hard, pigmented resin layer — the roof's color, shine, and UV protection in one. Florida sun breaks it down by oxidation: it yellows, fades, and turns chalky. Run a dry fingertip across the roof. If it comes away white, the gel coat is oxidizing and shedding, and that powder is what paints the white streaks down your sidewalls.
Chalking is cosmetic at first, but it's a warning. Gel coat does not grow back — every year it chalks, there is less left to polish.
Wash it like a boat, not a driveway
Wash it every three to six months — more often under trees — with a soft brush on a pole, mild soap, and a hose. Keep pressure washers away from seals, avoid direct sun, and wear shoes with grip: wet fiberglass is a skating rink. Skip harsh degreasers and abrasives; they strip the finish. While you're up there, look — a wash is also your inspection.
Removing oxidation: test a spot, don't burn through
For light to moderate oxidation, use a marine/RV compound made for gel coat. I reach for Meguiar's Marine/RV One Step Compound M6732 on a test spot first — it removes oxidation and water spots and brings the color back. For a roof gone fully chalky, Meguiar's Heavy Duty Oxidation Remover cuts harder.
Work small, check often, and stop when the shine returns. Compounding removes material — cut through thin, old gel coat and your options get expensive. Follow with polish or wax so the fresh surface isn't bare.
Protect it, or you'll be compounding again next year
Unprotected gel coat oxidizes right back. A UV protectant like 303 Aerospace Protectant every six to twelve months helps keep fading and chalking from starting over — cheap insurance on a rig that lives outside in Florida. Wax does the same job with more shine and more labor. Either beats a yearly rescue compounding.
The panel doesn't leak — the penetrations do
A solid fiberglass sheet has almost nowhere for water to enter. Your vents, AC, skylights, antennas, ladder mounts, edge radius, and end caps all still rely on sealant, and sealant ages out. Manufacturers recommend checking sealants every 90 days; at minimum, get up there twice a year and put eyes on every joint.
On flat joints I use Dicor 501LSW-1 Self-Leveling Lap Sealant, which adheres to fiberglass and flows out flat. On vertical edges, use the non-sag version. Keep silicone off this roof — nothing sticks to it later.
Spider cracks vs. cracks that matter
Spider cracks — fine lines radiating like a web — live in the gel coat only. Gel coat is more rigid than the fiberglass under it, so impact, flexing, and heat cycles crack the finish while the laminate flexes fine. They're shallow, they don't follow one straight line, and the roof feels solid underfoot. Fix them by opening each crack slightly with a rotary tool into a shallow V, filling with gel coat paste, sanding, and buffing.
A structural crack is different: one straighter, rougher line from a stress point — a corner, a screw, the roof radius — through the gel coat into the laminate. Press around it. Soft or spongy means water may be in the core. That crack gets ground out and rebuilt with fiberglass and resin. Sealant over it is a temporary rain plug, nothing more.
When a coating is the right call
If the gel coat is too far gone to polish but the panel is sound and dry, a fiberglass-specific coating can reset the clock. Dicor's system pairs Dicor Fiberglass Clean & Prep (RP-FCP-1), which strips wax, oils, and road grit, with Dicor Fiberglass RV Roof Coating (RP-FRC-1), a 100% acrylic coating applied in two coats. It's protection and appearance — not a leak fix, not structure. Fix every leak, crack, and soft spot first, then coat.
Mistakes that shorten a fiberglass roof's life
- Calling chalk a cleaning problem instead of oxidation.
- Compounding the whole roof without a test spot, then cutting through thin gel coat.
- No UV protection after polishing, so the chalk is back in a season.
- Silicone sealant on joints — it contaminates the surface for every future repair.
- Ignoring spider cracks until moisture gets under the finish, or sealing a structural crack and forgetting it.
- Coating over soft decking or an active leak instead of fixing it first.
A fiberglass roof asks less than any other roof on the road: wash it, keep the gel coat fed, seal the holes somebody cut in it, and read cracks honestly. Do that and it's the last roof that rig will ever need.
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