Cool beans!
No need to re-invent the wheel. Just design within this envelope.
The dymaxion uses flat glass in a teardrop.
Given that the Metro parts are sized to a given aero drag, if you improve the Cd, you can increase the cross sectional area. And the length:
If you follow the Dad's dune buggy plan, please replace the rear coils with something sized more like the front ones. Build to a show car finish. You know you're going to want to show it, may as well make that part of the plan.
Autospeed has some pretty good info:
Monocoque tubs
Building an Ultra Light-Weight Car, Part 1
Building an Ultra Light-Weight Car, Part 2
Tubing trusses
Building Ultra Light-Weight Tubular Frame Vehicles, Part 1
Building Ultra Light-Weight Tubular Frame Vehicles, Part 2