Fiberglass restoration questions

I have used an acrylic polish on my old fiberglass boat for years - it is a 1990 model, and the original gelcoat gloss was totally oxidized beyond buffing out, and I started using the "specialized" acrylic polishes (Newglas, Polyglo, etc.). They have the same active ingredient as the ZEP, but supposedly also include UV protection and other stuff to make them suitable for outdoor use and better protection of fiberglas. The problem with my boat is that it spends its life in salt water, the the horizon surfaces (the deck) take a real beating. While the topsides of the hull hold the shine well, the deck takes direct sun, and the coating needs to be renewed every spring. A few years ago, I started using ZEP on the deck instead of the high priced spread. Actually, it works out better on the deck than the pricey ones as it doesn't last as long. I have to renew it every spring no matter what I use, and the ZEP scrubs off much easier when I redo it. Our trailer is new enough that a good coat of quality wax once a year keeps it looking good, but when it finally oxidizes to the point that I give up waxing, I will probably go with one of the premium polishes to make sure it holds up the longest.