When I would recommend North Rim - the roads are closed for several months each winter.
You can boondock outside the park for free as this is perfectly legal in AZ.
If you like the thrill- go for Sky Walk.
Monument Valley is gorgeous and I drove the loop with TC on it.
I think I stretched the ordinance, but nobody stop me.
They have big parking lot, where you can leave camper and take a loop with truck.
The Valley Campground is very basic, so don't plan for luxury.
Mexican Hat in UT is worth stopping for pictures if you are not far away.
And my all-time favorite Lake Powell with all the Antelope Canyon, Rainbow Bridge, Horseshoe Bend and more.