Rig sounds totally uninspiring and generic. We already have rigs in real life pulling trailers. While Roller sounds like a kid's toy. I much prefer Warcage, like WarFrame but with an on-the-nose nod to Rollcage and really alludes to the destructive nature of the GRIP cars.
If not the whole concept of the cars being called "Warcage" then how about just one tank class car being called that?