Are you interested in stopping places along the way or just in Monument Valley?
Also, do you prefer full hookups, partial, or is some dry camping OK?
We've traveled the same route a couple of times and can help with some ideas that worked fo us.
The only place to stay in Monument Valley in June is Gouldings. They have spaces that can handle your 5er no problem.
https://www.gouldings.com/campground/
It will be warm there and Gouldings has full hookups so you can run the A/C and be comfortable. The Tribe has an "RV Park" by the hotel but the last time we were there is was a dry camp option. Feel free to pm back for more info.