KOAs are like Jellystones, might as well be at the local Motel 8
....we found a place call Rife Pit in the area that we found rustic, but exceptional. It was not too far from all the action and it was very quiet!! It IS rustic, so you'll have to have a full complement of gear on board, but it was beautiful. I still have the campground guide that it was in with all the info. If you or anyone is interested I'll send the info, just send me a PM.
We were last there a few years ago, so I am not sure with the economy that they kept it open, but I did find the local place that still would maintain it if it was still around. I planned on calling them when I planned the trip to the area in the future.
Hope you got to get to wall drug and Crazy Horse! Both neat places to visit. Also the spring fed pool in hot springs and wind cave were fun as well.