Ed, I add some caulk to the belly area of the fish to fill it out naturally. I do this by taking a tube of caulk and placing a piece of clear tubing over the end of the caulk tube. It helps to heat the end of the tubing with a heat gun first. Then I insert the tube into the anus of the fish, filling it to suit. Then I take a small piece of paper toweling and stuff it in the anus, so the caulk reimains inside. Then I proceed to mold the fish on the 1st side. I do not do anything to the fish prior to freezing. Taxi-lover, The material I use is play doh (for the clay...home made or store bought), and Reo-flex 40 dry for the mold material .