paint will stick fine to fiberglass. if you don't have spiderweb cracks in the gelcoat, you can just sand it with some 320 grit and paint away. if the gelcoat is cracked. you will need to sand almost all of it off then use a good high build automotive primer/ filler, or primer/ surfacer. then sand that with 320 and paint. if you sand through the gelcoat (you'll know cause it will pull fibers out like lint that won't go away) you have to REALLY lay the primer to it, sand it down and prime it again till the lint goes away, then sand and paint
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