With a foam hull your going to have to be very careful when fibreglassing - Polyester resin will eat the foam, epoxy resin is safer, but even that will attack some foams....
Best bet would be to cover the hull when the final shape is achieved - try papier mache (strips of newspaper glued on using wallpaper paste) 3 or 4 layers thick - Leave it to dry for a few days and it will form a hard shell that can then be sealed and painted to give a decent finish before fibreglassing.
Regards
Eddy