I'm dropping here the idea that, actually, the 3rd manufacturer could make them out of weird alien monsters "harvested" or "enslaved" into cars (dead or... still partially alive)!!
Think of it as an organic entity embedded in armor with the feel of a:
- Half Life 2 "Combine tech" + Doom + Evangelion kind of mech
- The car would have a sort of spine along its length and you'd see its "ribs" partially
- When damage is done to it, you'd see its flesh beneath the piece of armor gone
- Instead of pissing oil, it could bleed
God knows our mighty devs have a lot on their plate, but yeah... ideas n stuff