The main thing you have to watch for buying epoxy is wether it contains solvents, which could cause a problem for the polystyrene foam. I would not recommend to use polyester resins, because they contain solvents that will damage the foam.
Any water based paint, that includes the water based polyurethane resins/lacquers, can be used to cover the polystyrene for floating rafts. Read the ingredients on the package and you will know if it contains solvents.
For a good job with resins and glass fibers use a special roller (you can make them out of washers if you like) and a short haired brush to tamp the air out of the glass fiber mats. The Gougeon Brothers (West System Epoxies) are a very good source for further study. Here is a link to their book
http://www.westsystem.com/ss/assets/How ... 061205.pdf. Look for the chapters about applying epoxy.
Main thing is, first roll on a nice layer of resin on the foam, than put the glass fiber mats on and roll/tamp out the air. Then immediately apply a following layer of resin to saturate the glass fiber mats completely. Make sure no air will be trapped in the layers. You'll have to work a bit fast to avoid the first layer hardens and you can no longer put the next layer of resin on.
If that happens (hardens while you work on it), let it harden out for 24-48 hours, sand it rough and apply the next intended layer of resin. In hot weather use a slow hardener, in cold weather use a fast hardener. Make sure you mix the components thoroughly, scraping of the sides and bottom of mixing pot regularly while you mix. Do not mix more than you can handle within the reaction time. Preferable, poor the mixed resin out on a larger surface to avoid too fast reaction (leaving it in the pot while you hold it can speed up the process with possibly very strange results like smoking resin that suddenly hardens to jelly and consecutively within seconds to a glass hard substance).
Did a lot of boat building with epoxy and find it easy to work with, once you know what to do with it.
Backyard Aquaponics
