Try the Mt. Rushmore?Hill City KOA. We were there in 2006 and found it to be a very nice campground. Spotless, facilities were great, all-you-can-eat pancake breakfast. Would definitely go back again!!!
Another possible site is Hart Ranch just south of Rapid City. We visited there and had looked into a time share at it. Very nice spot with a great golf course nearby. I think they will take non-members for short stays. You can check it out online at http://www.hartranchresort.com/welcome.html
We normally stay at the Rafter J Bar campground. I know you did not ask for other than campground info but you should add Crazy Horse and Custer State Park (including Needles Highway) to your list of must see's while in the Rushmore area. The roads can be narrow and winding through Custer State Park so leave your camper at the campground.
We were just out there last year. We stayed in Custer State Park(Game Lodge Section) the only hook-ups was electric and the Game Lodge is the only section fenced. This section does have black top pads and a water hook up for the grounds. It's nice to be in the park because everything is drive. The other sections are much smaller and the buffalo roam around your site.Go to Sylvan Lake when in Custer. We also stayed at Elk Horn Ridge RVResortin Spearfish. It's a brand new campground (I mean resort)<5 yrs. old. Full hook ups, concrete pads with patios, 3 sewer hooks at each site, cable, very nice pool andtheshower houses are spotless. You actually get yourown bathroom (toliet, shower, sink) all behind asolid door. It's very nice, but no on-site fire pits. We also had to spend the night at the Rapid City KOA due to mechanical issues. They were very accomindating and view looks South over Custer and Rapid City. It's very typical KOA.
I am sensing a "theme" with all U can eat pancake breakfast's
Yea, to bad they didn't have all you can drink beer night while we were there!! But yea, there is a theme developing.
Below are some pics from campground; the check in desk, inside the store, a view coming in the campground drive, a comfort station (laundry and bathroom), playground & us while at Mt. Rushmore. Not really a typical KOA, this is a campground KOA should be proud of.