There have been other excellent posts on repainting a CC fiberglass roof, so I'll just try to add our insights to those already posted. The best thread we read was
this one when doing our roof.
Our '00 Magna's roof was in rough shape cosmetically - with a lot of deteriorated gel coat leaving a chalky mess & small black spots. No cracks or damage to the integrity of the fiberglass, luckily. Our lap seals needed redoing, too, and we took the opportunity to install new MaxxAir Deluxe fans in the galley & toilet room while the sealant was off. Those fans are a HUGE improvement over the originals from CC, that's for sure!! Anyway, hubby (James) removed and replaced all sealant on everything on the roof with Dicor self leveling lap sealant. He also removed the old TV antenna & blocked off the hole, then added a plate that he Dicor'ed down (& a solar panel ended up in that spot, valuable real estate!). He attached the solar panel mounts with VHB and then Eternabond to the bare fiberglass, before painting.
We decided to use Interlux Brightside marine deck or "topside" paint in bright white. This paint is a cult favorite of Safari owners (also a fiberglass roof). We got 3 quarts but wished we'd gotten 4. We ended up ordering a 4th to recoat a spot and for the eventual painting of the solar wires. We did not opt for a primer, based on my research. YMMV. We cleaned, and cleaned, and cleaned again with Simple Green. It took a lot of time & effort to get all of the chalk & black spots removed and down to the bare fiberglass, but they say surface prep is everything when it comes to painting, right?!
We did two coats of the Brightside, with 24+ hours to dry in between. The one mistake we made was painting a bit too late in the day. It was October in NorCal, so low 80's during the day and 50's at night. One area that was at the rear of the coach, so last to get painted, dried with a haze and not a gloss like the rest. I emailed Interlux & they promptly replied, having looked at my photo, to tell me we must have painted too late in the day and dew settled on the hazy areas, and to repaint that area. I told them nothing about when we painted, so the response was spot on. We did repaint just that section (much earlier in the day) and it looks glossy & awesome like the rest. Like I mentioned, James also decided to paint the wire runs for the solar with the Brightside, just cuz we had some left and why not, for some UV protection (which is one of marine topside paint's benefits). We also painted some but not all of the Dicor sealant, for more aforementioned UV protection.
We got absolutely blasted by windy rainstorms in Moab the last two nights & so far, so good - the roof & new seals all seem watertight (not our slide, so much...we learned the hard way to bring that in if a windy rainstorm is expected).
Time will tell, but folks say they get a good 5 years out of 2 coats of Brightside. To us that was a much better proposition and not much more work than an annual coat of wax. Luckily it seemed our roof had never been waxed so we didn't have a bear of a time trying to remove that to prep the surface. Again, and as always, YMMV but this here's an account of our mileage. Thanks for reading! Ask any questions!
Before & after photos, may need to zoom in: