see your Welcome post ...
awe heck - I'll copy/paste here ...
Hi John. Welcome to the forum! I tow with a Cummins, too. Grew up in Custer, SD but have been away for so long that I don't have any relevant experience staying in the campgrounds up there.
We were up in the Hills last weekend (caring for sick family - so will have many more trips) and drove through the front part of Palmer Gulch, which looked nice. I know it's gotten good reviews. In KOA tradition, the spots are close, but not nearly as close as some!
We had a family reunion in Jackson Hole, WY and a non-RVing family member picked a KOA up there that had the spots so close, that our slide out touched the awning of the neighbor.
Apparently all those KOA campground guides running around in their golf carts are as much for their own protection as they are for camper's convenience. Spots are so tight that they guide everyone!
Right on the corner of Hwy 16 and 244, I noticed Rafter J Bar campground looks like they've done a lot of upgrade and remodel, but didn't drive thru.
Horsethief Lake is just a few miles east up the road from Palmer Gulch, towards Rushmore, and has a National Park campground (or did?), but I have no idea how many sites it has any more, nor any idea about reservations. Used to be a nice little lake for trout fishing.
If you like fishing, consider a trip up to Deerfield Lake - Deerfield Road exits Hwy 385 to the north west on the north end of Hill City. Nice drive and nice lake.
Other things to see and do - Hot Springs Mammoth Dig, Evans Plunge, Wind Cave National Park (and maybe the cave, but I always recommend Jewel Cave west of Custer over Wind Cave), Custer State Park (and the Wildlife Loop Road), Game Lodge, Needles Highway, 1880 Train, Spearfish Canyon drive... ah sorry - got carried away. One could spend all summer exploring the Black Hills and not see it all.
Anyway, hope you enjoy the Hills on your visit ... I'll wave from I-25 as we pass thru Cheyenne again ... looks like a trip almost every weekend throughout the summer for us.