[Christ]

This one's a prototype, right?

Prototype vehicles are NEVER built with top-end materials. If it's a test bed, build it how you need to build it to get it done, show it off, campaign and get funding to do it better for the /real thing/ later.

I see no reason to not use something that will work in the short term and save money on a prototyped design. If the design fails during testing, you upgrade it and move on. The general idea is that it will be a completed vehicle, able to be seen, felt, shown, tested, admired, photographed, and invested in for some sort of production, and/or the design sold [probably not, I guess] to a company who can produce them en masse for sale.