Yep I use drylok on mine as twentyleagues said. I can't speak on the fiberglass resin though because I also use clear pond armor on my foam backgrounds. Drylok does form a nice hard coating though so I would "think" (cant say 100% sure so I would test a small scrap piece first) but I would think if you did 2-3 coats of drylok first then you might be okay to use the resin over it then.