Themed trips are a wonderful way to enjoy the RV lifestyle. No - we are not planning any for this year.
But - your cowboy theme is great. We have traveled most of that country and several things come to mind:
While in the Dakotas be sure to take in the ND Badlands - Theo. Roosevelt National Park.
Waterton NP in Alberta should be on your route. From there take Highway22 from Pincher Creek to Cochrane Alberta. Our favorite cg is Bow River Edge CG in Cochrane. Great western Alberta ranching/ cowboy museum there. And easy access to the Calgary Stampede via light Rail (station close to that CG. Reservation required there always but especially during Stampede time ( do it now!!)
Back on Highway 22 - be sure to stop and take in the Bar U Ranch National Historic Site
Also - in Pincher Creek see the Kootenai Brown Museum.
Other special site may come to mind later. PM me if you want more details.
John