thanks for the suggestions. I was having a hell of a time finding ANY suitable material from plastics companies, art stores, big box stores, or upholstry shops - at any price - then went to a local craft chain called Michaels. Found a 3x5 roll of black plastic foam for about $7.00. Bought a few rolls and after some experimenting found that gluing two together gives it some stiffness and still shapes with heat gun.
