Not sure about your route, but Montana Wyo would be on my list depending upon where you are going.
Yellowstone and Glacier, also the Black Hills SD area is nice...
Glacier is closed - they are still plowing the roads. Takes a L O N G time.
YNP is open, but the Beartooth Highway is still being plowed - will open on May 27th.
Glacier is great, but with an rv likely cannot traverse the going to the sun road.