We were in both the Black Hills and Badlands NP a few weeks ago. We used the Visitor's Bureau free map extensively. The whole area is very well signed!
"Don't Pet the Fuzzy Cows!"
While there we saw many 40' Class A on the main road loop in Badlands. I'd rather not take my 30' trailer but it's not impossible.
The Black Hills area has 3 roads that are not for anything of any size. They are fantastic scenic roads that are very well signed and far from necessary. 8 - 9' wide and 8 - 11' tall tunnels are far worse than the tight corners and 'pig tail' overpasses, even in my pickup. Bypass the Iron Mountain Road, Needles Highway, and Peter Norbeck Scenic Byway and you will have a great time!
https://www.dangerousroads.org/north-america/usa/2737-needles-eye.html