Not going to be much help as far as CGs go, we stayed in Hermosa(hwy. 79) and roughed it w/full hookups at Heartland RV Park and use the Jeep to explore the area. We went to MT. Rushmore, of course, and then drove into Keystone for a buffalo burger. They're very tasty critters.
We traveled the Iron Mountain and Needles hwys. in both directions...the sight of Mt Rushmore visible from inside the tunnels was very cool(Rushmore is visible from all of the tunnels, just have to be going in the right direction). No Class A's will fit in the tunnels but both of those highways are not to be missed. Rent a car if necessary...very curvy with some amazing topography.
We took a long tour of Wind Cave...on approach, we got lost on a dirt road
in the Southwest section of WC NP and somehow ended up at the cave, so we took the tour and it was well worth it. We also explored Custer State Park, but saw more buffalo at Wind Cave. The roads were good for RV travel in both parks had we not had a toad. Also, Badlands NP isn't too far away and is RV accessible as well. We could have stayed another 10 days in the area...lots to see. IIRC, we saw a few CGs at both WC NP and Custer. Have a great trip. Bob