Need suggestions for rebuilding large cargo door

What is final finished thickness of the door? I would consider a 1/4" sheet of luanne, cut in half, and a 1/2" foam board. Use hi-temp contact cement to laminate the luanne to each side of the foam, then again to laminate the fiberglas or filon to the outside piece of luanne. That should be plenty strong for a cargo door. Use some plastic U-trim to seal off the edges with silicone or geocel.