FYI - another opinion here. We have workamped the last two summers in Custer, SD at Buffalo Ridge Camp Resort. We are returning for a 3rd season this coming spring/summer.
We absolutely love Custer, such a quaint small town.
Both Rafter J and Fort Welikeit are great recommendations as well.
Buffalo Ridge Camp Resort is about 1/2 mile from downtown Custer. Access to the Michelson Trail (bikes, hiking trail) is right across the street from the campground and the trail goes right into downtown Custer.
Campground is 6 miles from entrance to Custer State Park, about 15 minutes from Mt. Rushmore as well.
We are a Good Sam Park, all pull thru gravel sites with full hookups and complimentary wifi, no cable.
Best time to visit the area and avoid the crowds is definitely after Labor Day. Just be forwarned that it can be chilly in September in this area, they seem to go right from summer into winter!
Many places close down after Labor Day or reduced hours and most campgrounds are closed for the season after Buffalo Roundup which takes place the last weekend in September.
You will love the Black Hills area, so much to see and do and friendly!
Depending on where you will be arriving from suggest you stock up before arriving, Rapid City is the closest Walmart and that's about an hour drive each way. If you plan on being in the area for a while you can order online from Walmart with free delivery, that's what works for us spending the summer there.
Enjoy!
Susan