I used epoxy over polyester for a Greenland skin boat 3 years ago. If you go to the site below , crack open me (Jay Babina) and Dean Bertoldi who both used epoxy on our skin boats - built the same time.

http://connyak.org/Boatbuilders/Yakboatbuildersframe.htm

Mine has held up fine. no cracks, still has flexability and the abrasion resistance is tough. I've gone over barnacle covered rocks with it. I have two coats on it. Many skin boat builders are re-coating and having trouble with leakage. This workded out great although I think an ideal covering would have more flexability. It's like thin poster cardboard. Epoxy (colored) was too shiny so I gave it a light coat of matt varnish from a spray can (Helmsman). I guess that would help with UV as well although it's not my regular kayak - I use it on occassion. I guess the dark coloring helps with the UV too.

Next time I would try colored varnish only for the convenience and maybe paint a coat of epoxy on the abrasion areas on the bottom.