I used a formech vacuum former with a sheet of .010" PETG, which is the material used in RC car bodies...therefore it is rigid and durable for the thickness and weight.
I can get an ek civic for 1500-2000, which is cheap enough to chop up without worrying about losing a ton of resale....an insight would be another animal, and maybe one I'll tackle down the road. I've also toyed with the idea of an EV, which I may have a lead on a prebuilt project one belonging to bennelson on this forum.
As for underbody paneling, I have built partial trays on race cars in the past, but that was to help optimize a front diffuser.
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