Black Hills, Mt Rushmore

This state has BEAUTIFUL state parks that offer huge sites and great camping. But keep in mind that they are electric only. No water hookups.
We are going next month and we are staying at Spokane Creek Resort which is in Keystone. Another fairly centralized place. Your length is a factor at some places but most importantly in your travel. Wherever you book make sure you call them and ask about directions. I cannot stress this enough, DO NOT RELY ON GPS. There are roads through the Black Hills that will not accommodate your rig. On the Spokane Creek reservation email I received it specifically gave directions and said do not use GPS as you will end up on sections of road that have turns and too tight for most large rigs.

Here is where we are going. http://www.spokanecreekresort.com/

Make reservations asap to get your best choice of sites. The first week in July is the busiest of the year for families.
The new site for combined private & state camps is www.campgroundsd.com
It is live now, but not yet found by all search engines.

We're going back to The Beaver Lake Campground in Custer this summer. The grand kids really like the pool & waterside. We really like it!

http://www.beaverlakecampground.net/

http://www.youtube.com/watch?v=uocUFz8oZwo

X2 Rafter J, and Hill City is fairly central to those places you've mentioned. Have a great trip to one of my favorite areas!

Happy Holidays Resort. Nicely wooded, fits large or small units, quiet.

http://www.happyholidayrvresort.com/

We're staying at Rafter J in June.
Done Hill City KOA a couple of times, very nice (and very big), but we heard Rafter J is better yet! Can't wait!

If you do KOA, there is one very close to Rushmore that is very kid-friendly. Lots of activities on property. Very near Rushmore, central to Custer State Park (do NOT overlook this), Deadwood, Wind and Jewel Caves. If you prefer more natural site, there are 3 (if I remember correctly) campgrounds within Custer.