A while back, I saw a "custom car" from England that had all home made body panels - it had begun life as a Pajero and the owner scrapped the body (for whatever reason) retaining the floor, seats, dash, and windshield. For the rest he built a wooden frame, stretched pantyhose, and laid glass.
Came out looking pretty silly, chiefly because of the fiberglass "hanging" and forming concave surfaces between the frame pieces - but it sure did look lightweight. Not sure if this helps your idea along at all but there it is
