+1 on Red Lodge, MT. I stopped in for the night last July, walked to the Yodeler hotel, then up the street for beer/food. Just a nice place for an overnight.
Then you gotta hit Johnson Creek, ID. Because, duh, it’s Johnson Creek!
If you end up towards Seattle, look at Auburn (S50) just south of SEA as a good overnight stop; park on the south transient ramp and walk 100 yards to the Days Inn. I stayed here for 2 days while flying around the Puget Sound area; it’s not fancy, but convenient as a hub while out flying around exploring.
A stop I made for absolutely no reason at all was at Porthill, Idaho (1S1), way up on the Canadian border. There’s nothing there but a gas station/store and the border crossing, but it’s just a lovely grass strip set in a wide valley surrounded by big ol’ mountains. For me coming from the Texas Gulf Coast, that was all the reason I needed.