On the way to Rapid City, I stopped at the Agate Fossil Beds National Monument.
Wonderful museum and a nice hike up to the beds. Plenty of RV parking.
Then on up to Harrison NE where they have a very nice city park with 2 spaces with electric and water and showers and restrooms in the park. Donation Box.
Next stop was Fort Robinson State Park by chance. I was on my way and there it was. They have camping, lodging food, and wonderful museums. The Grounds are large so be prepared for a good hike. This area has a wealth of information on Red Cloud one of the most important leaders of the Oglala Lakota from 1868 to 1909.
Next Stop Rapid City SD