Like Bob, I used the Kilz as a primer, mainly to make sure the topcoat would adhere really well, I didn't have mold, but it was ugly. Then, I painted with an acrylic EXTERIOR satin. I choose the exterior because of possible temperature changes. It's two years later and I've had zero peeling and it looks fantastic. I painted with a small, sponge roller and was able to get it all done in a few hours.
A few weeks ago, in an effort to freshen up the countertop area, I used a polyurethane floor paint in a semi-gloss on the
fiberglass. It's the same paint that I've used successfully on my laundry room floor that looks great after about 5 years. I hope to paint a design on it this week and may clear coat it all depending on how intricate a design I use. When I have my clients walls faux finished, I often add a top clear coat. I prefer that coat to take the bumps and bruises and know that it really does extend the life of the faux finish.
Good luck!