camping policy at national parks

I occasionally wonder about the tent sites. As I understand, typically tent campers will setup their tent, an sometimes work out of their vehicle. Sometimes a camp stove on the tailgate of a pickup for example. I have seen some leave there supplies and ice chest in their vehicles.

If a person's vehicle was a TC, would they be allowed to they camp in the same manor? They could not run a generator, unless it was allowed in the tenting area. They would have to setup a tent.

I am not asking this question as a troll, but just something I have wondered about.