Sounds like a wonderful trip! Glad you already have reservations in the busy spots. I second the suggestion for the Rafter J Bar in the Black Hills - and the Hills are so much more than Mt. Rushmore! Don't miss the Crazy Horse memorial! There's an old steam train one can ride there, lots of hiking/biking trails, etc. Depending on the size of your rig, Custer State Park has some nice campgrounds as well, some with electric hookups.
A couple other spots I'd recommend seeing: Devils Tower in n.e. Wyoming and Little Bighorn National Battlefield - both are between the Black Hills and Cody/Yellowstone/Glacier, the latter being just off I-90. The KOA at Devils Tower is right at the base of the tower - great view! A couple nice CGs near Little Bighorn; it's worth a day to tour the battlefield, which you can do on your own as well as with local guides. Don't miss the hourly ranger talk(s) at Little Bighorn.
I don't advise traveling US 14 (and especially not 14A) or Beartooth Hwy with your entire rig - just with the toad/tow vehicle. Beautiful drives but very tough with RVs.
