Fiberglass is paintable, but it's not a simple matter. It's an industrial process. Suggestions for expensive industrial paint
sound like the only way to go. You can't expect acrylic to stick for long. It'll go on. It'll look nice for a while. But it will peel by and by for sure. It's just not very adhesive. If you're going to go with hand painting
of any kind make sure to sand the surface first.
As for floor finish, I agree with those who say it's for floors.
If I wanted a design on my trailer I would go with a wrap. The possibilities are endless. I can't speak for the longevity and problems of removal down the road, but the few I've seen sure look great.