When you are out at Badlands, hit up Minteman MIssle NHS. They do offer tours of a silo, but they can book up a ways out. Even if you can't get into the tour the center is worth some time, at it is at one of the exits of Bandlands.
I think it is required that you stop at Wall Drug too.
If you have time in the area, hit up Jewel Cave and Wind Cave as well, you can do those in a day and possibly tacked on to a visit to Mt Rushmore, depending on what all you want to do. Our group liked the evening program at Mt Rushmore.
But my favorite part of our trip to that area was Custer State park. Lots of wildlife watching and a very scenic drive. Got my favorite picture of my daughter at a stop on Needles Highway. If you are doing a RV, it may not be as much fun.
Side note, get a national parks passport stamp book too if you visit a lot of National Parks (or want some motivation). It's fun way to get some free souvenirs when you visit. We started a few years ago with the small blue one, but I really like our new "
Colletors Edition" one.