I would use epoxy though I personally prefer poly as I have had a lot of experience working with it at the boat factory. The reson I would go Epoxy it because polyester resin generates a lot of heat and over plastic may react with it. Or you could use Polyurethane to glass with which is just as good as epoxy and I use that to glass all my planes. Epoxy is just too expensive and polyurethane gives a lot harder surface.

Joe