Three years ago we took 2 grandkids 6 and 8 for 30 days from NH to:
Shipshewana
Colorado Springs
RMNP
Moab
Bryce/Zion/Capitol Reef
Williams (train to grand canyon)
Dandridge, TN
This past summer we took 4 grandkids from NH for 30 days (4,7,9 and 11) to:
Black Hills
Yellowstone
Grand Tdetons
Moab
Durango
Both trips were from the middle of July to the middle of August. The kids loved Page (went to the north rim from there). The 4 grandkids was a little long for grandma and grandpa but not for the grandkids.
We did this in a 45' MH and had reservations for all the major stops. I would not do it without reservations at must stops. On the way out and back it was Walmarts or CG's. Coming from NH, I'd plan on 500-600 mile days going and coming. That's easy highway driving.