I hope you have a great trip. I do have a couple of more "low-investment" suggestions for you to see on your trip. By "low-investment," I mean they don't take a lot of time, a lot of driving, or a lot of expense, but deliver a pretty impressive return on that investment.
If you find yourself on I-90 at some point between Bozeman and Butte, the Lewis & Clark Caverns State Park is certainly worth a peek. You don't have to actually take a caverns tour, although you can do that if you like (personally, I've seen a number of caverns and they all kind of look the same to me). What I like about the park is the great views from the upper visitor's center looking out over the Jefferson River. There's a nice little cafe and gift shop and the top and some really great photo spots. The road to the top is winding, but it's a nice paved road that RVers navigate just fine. If you are driving west on I-90, you'll see signs for the caverns at the Three Forks exit, but drive on another 20 miles or so to Cardwell and take that exit. The drive between Cardwell and the park follows the Jefferson River through a pretty impressive canyon. It's only about 15 minutes from the interstate to the top of the caverns (not counting photo stops), but it's a drive that gives a tremendous bang for the buck.
If you plan to stop in Butte anyway, travel up main street through Uptown and take a little detour to the Granite Mountain & Spectacular Mine Disaster Memorial. 168 miners died in the two mines in 1917 in the worst hard-rock mining disaster in US history. Butte sits on the side of a huge hill, so the upper parts of Uptown are several hundred feet higher than "the flats" down by the interstate and the memorial sits even higher on that hill, several hundred feet above most of uptown. There's a pretty good audio interpretive display up there and some good views of the mines and city below. It's usually pretty windy up there and several degrees cooler than the flats down below which adds to the somber, almost surreal environment. If you stop at the Butte visitors center off of the Montana Street exit, they can give you information about, and directions to, the memorial. One interesting little fact about the disaster: it occurred in June of the year, but rescue efforts up on the surface were hampered by a significant winter storm.