We did this exact trip last year (plus Yellowstone and Cheyenne).
From Milwaukee we stopped for an overnight at Cabela's in Mitchell. Then we stopped at Corn Palace before hitting the interstate in the morning.
We stopped in Murdo for gas and a 2 hour walk thru tour of the Pioneer Auto Museum.
Then we entered the Bandlands, took a few hikes, and slept at Badlands / White River KOA.
On the way out the next day, we drove 240 (to Wall drug) we drove into SAGE CREEK RIM ROAD. This is a gravel road and drivable with an RV, but you dont want to go far nor do you need to. IT IS the ONLY spot you will see Wildlife in the area. There are turn around points, but if you are not comfortable...just dont do it. Park along side 240 and walk in just a 1/4 and look to the south in the valleys.
On to 3-4 hours at Wall drug and the general shopping area, then to Rafter J's for a 5 night stay. No complaints here. Its a good campground for the area, but they do not serve food like they used to. They do have a nice store.
We did the Blue Bell stables horse ride, which was fantastic. The Jeep tour, which was ok, as you can see most things in your own car on the Wildlife loop, but the Jeep takes you some places you are not allowed in your own vehicle.
We did an UTV ride with the whole family, if you're comfortable with these machines and know how to read a trail map...this is a MUST DO. It was one of the unforgettable s for us.
Mount Rushmore was incredible, and we went back a second time for the night show which was a great site and the show was ok. The Crazy Horse night show can be missed...for sure! Its too long...super boring.
Got kids and like zoos? Bear Country USA. Unique drive thru zoo with a walking portion at the end. Go very early or very late.
A few less traveled sites and fun things to do with family; Black Hills Wild Horse Sanctuary, book a tour ahead of time. And on the way back, you MUST stop at Cascade Falls. Bring your swimsuit.
Need a beach day? Angostura Recreation Area. 100% worth the drive. We actually ended our day here from the Wild Horse Sanctuary. It was awesome sauce frosting on this day.
