Some tips: use Google Earth if you have not yet when planning your trips. Everytime I see something interesting I decide how interested I am and use Googel Earth to mark it. Purple is really want to see, Green I would like to see and Light Blue stop if in the area Yellow or White just something I'm mildly interested in. That just happens to be the order of the colors of the placemarks. It makes it easier to see where I want to visit when I'm looking for a trip to take.
In the Mount Rushmore area. Bear Country but not in the middle of the tourist season to hot and lots of people. Needles highway (but not in your motor home use the tode), Pioneer Auto Show http://www.pioneerautoshow.com/ (if you like cars it will take you 4 hours to see them) Spend the night there. You are less than 400 miles from Cody Worth the extra week to go there in my book. Besides the Buffalo Bill's Historical Center (if you want to look over all of the guns it is a two day stop) take in the Irma hotel http://www.irmahotel.com/ wild west gunfight spoof. Recommend you stop in and purchase reserve seats that put you in the front and do not cost a lot. But a highlight often missed by people visiting Cody is the Old Trail Town http://www.oldtrailtown.org/ out west of town.