You have to use epoxy to start with since this is the only resin that will work on top of polystyrene foam. The polyester/styrene based resins will dissolve the foam.
Once it's coated with the epoxy (with or without glass?) then you could use other resins, I would consider the Duratec Sunshield. It's UV and specifically made to coat over epoxy or other resins. If you want a clear?
If you don't need clear then it could be coated over the epoxy coat with with a polyester flow coat to any colour you need. Tough and durable. You might want to do your own small sample just to test the adhesion between the epoxy and a polyester.