I had a couple of thoughts regarding the body for this car -
Aluminum (relatively easy and light, but may be expensive)
Fiberglass (slightly heavier, but more 'moldable', about the same cost as aluminum
Canvas (like an old aircraft / canoe) Cheapest, not sure if 'canvas dope' still exists.
Apparently BMW has a prototype with a canvas body that can change shape by moving inner ribs.
Shape shifting C-Car? 8-)
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