Idaho & Montana Trip

Idaho's Sawtooth Mts are well worth the stop, as is Craters of the Moon Nat'l Monument, if you haven't been there. (That's more south-central Idaho, but perhaps could be on your route.) The McCall area of Idaho is gorgeous!
Camping in/near the Sawtooths is pretty much no-hookup; we've looked at a couple of CGs in/near Stanley with hookups and were not impressed. However, there's a dandy little RV park with water & electric hookups in between Stanley & Challis, called Torrey's. It's on the Salmon River in a canyon (little to no phone service or wifi). Beautiful spot and a good base camp for a few days from which to visit both Stanley & Challis, plus some old gold mining ghost towns and the gold dredge. With no big trees, this CG would fit your rig well. Only about a dozen sites, so reservations advised.
We haven't seen the private CGs in McCall, but if you can snag a site in the RV section of Ponderosa State Park, it's WELL worth visiting. Beautiful wooded CG on a lake, and the RV sites are all FHU, I believe, and just as pretty as the "regular" ones. It's extremely popular, so reservations well in advance are essential.

I found the Havre Beneath the Streets tour (Havre, MT) fascinating. Reportedly, the Wahkpa Chu'gn Buffalo Jump there in Havre is also exceptional and unusually well-preserved; I didn't have time to visit it myself when going through the area.

The Nelson Reservoir campground, a spell to the east on Route 2 between Malta and Saco, is a pretty public campground with no hookups and minimal amenities, but also available free of charge. It's on the shore of the reservoir and has some trees and just generally pleasant surroundings.

Without much effort you could travel through Idaho Falls and into West Yellowstone (or into the park if you like dry camping) and enjoy all of the amazing things Yellowstone has to offer. The only bad part is the timing as August is prime tourist season and all the buffalo and elk have retreated to higher ground. Still a great bucket list journey if you have not done so in the past.

Find the RV parks you want to stay at, and make your reservations NOW! I had to make a trip to Kalispell in August to attend a funeral. The only spot I could find was in a relatively new RV park on the Hwy 93 bypass South of town. $120 per night! There were several empty spaces there; why was obvious! I posted a review in the campgrounds forum here.
I know how hard it is to plan that far ahead, especially when you are unfamiliar with the area you will be traveling through. However, it seems these days it is almost a necessity.
Without knowing the highways you will be traveling, it is difficult to say what you might like to stop and look at. There are museums almost every where that are worth visiting. Deer Lodge is one such place, Missoula is another, Billings is worthy of mention, Kalispell is another, as well as Polson.
Cody, WY has a great museum, if you are interested in guns or Buffalo Bill or Western art. The Homesteader Museum in Powell, WY is great, too.
Idaho Falls has one of the largest Military Surplus stores in the country. I could spend hours in there wandering around and looking! In fact, I have done so!
Again, plan ahead, and good luck.