yeh everyone has this problem i think.
Please correct me if im wrong.
All i done with mine was fiberglass the back also put a bit of tigar seal on first for a bit of strength, then filled the front with clear silicone to give the impression of the foam, that was in there at one point (also make it soft to the touch) it took a bit for the silicone to go off, but looks very good, will try a get some pic up.