Is it possible to stay in campground if sleeping in car rather than in a tent?

You can. The campground next me when I went, the guy was staying in his VW Bus.

I always sleep in my van at Zion, you can use your campsite however you want.

I think it is not allowed. If you have a camping place reserved your free how to use it I imagine. But sleeping on the parking is not ok

Yes, you can sleep in your car

yes. there is not a restriction that uou have to sleep in a tent. when you get a campsite, you are pretty free as to how you use it. just don't bother your neighbors.

You should be able to no problem. But to be 100% I would ask a ranger when you go through the park entrance if you can.

That wont be an issue, as long you at least have something on the campground and dont leave it empty, they'll be fine with it.

Yes sleeping in the car would be acceptable.

Yes, you can sleep in your car if you like.