My idea:
Fore and aft ends are 36" dia 3/4" plywood. Floor and support also of wood (3/4" ply floor, 2*4 supports).
Aluminum 3/4" angle running lengthwise, covered by .032" aluminum skin. Port side shifted aft to reveal interior.
Upper angle on each side would probably need to be steel rather than aluminum in order to beef up the structure some.
Seat structure, interior bulkheads made of ply (shown tan here for clarity, all interior would actually be painted chromate green).
Real basic but I think it gives more of an aircraft feel than all wood construction.