Bill, I've had great luck with Easypoxy one part polyurethane.....did it on an older fiberglass sailboat....over gelcoat....came out looking like a professional spray job...and it lasted very well......lots of color choices...runs about $20 per quart at West

fill any scratches, lightly sand the whole boat with 250 or finer grit, roll it on, and tip it off with a brush......very durable, holds extremely well to the glass or gelcoat.......they sell an undercoat also, which i didn't need to use

good luck