An older thread, but I just found it!
We went last July and stayed at Blue Bell in Custer State Park in our a-frame. It was one of the nicest state parks we've ever been to, and I'd highly recommend Blue Bell. We went through the other campgrounds in Custer, and they all looked really nice.
It's a nice campground, but also has a lodge with a great restaurant, and a nice camp store. It's actually the equestrian area too, and you can do some horseback riding if you want.
There is a lot to do in the Black Hills area. Here are some things we enjoyed:
Downtown Rapid City has some fun restaurants and shops.
There's a museum at Ellsworth Air Force Base. It's small, but fun to see and doesn't take much time.
You can get a tour of a Minuteman missile launch control facility, check the NPS.gov site.
The little towns like Custer, Hill City, etc. can be fun.
Bear Country USA
Crazy Horse is neat, but I might just see it from the road and not spend all day there.
In Custer State Park there are a some great roads to drive, though maybe not with a trailer! Iron Mountain Road and the Needles Highway.
There is a "wildlife loop" drive in Custer, with lots to see.
Deadwood is fun, but more fun without kids!
Do some planning though, because it's a lot of driving to get around! It's a big place, but the windy slow roads are the real problem.
2014 Rockwood A122BH
2014 Nissan Pathfinder