Besides automotive paint
, the only thing I would "paint" a fiberglass trailer with is Magnet Paints Monstaliner. I have no association with them, but they make the best damn coating out there. It's a UV permanent truckbed liner. No cheap/sharp crumb rubber. It's smooth, but wavy. You could apply it completely smooth too if you use a brush. You can also spray it for a more aggressive texture than the roller. You can get it in all kinds of colors, and it adds strength to the shell. I will be going this route on my Scamp
16. Not sure yet if it will stay white, or match my soon to be monstalined vehicle with "Road Rash" (insanely bright Orange.)
Oh and this stuff is AMAZING for floors too.