Hill City SD to Devils Tower, WY

Actually there is. Devil's Tower View Campground is a few miles from Devil's Tower. No frills. Pull thrus with water and electric only but close to the highway. Nice restaurant on site. Probably a better view then from the KOA. Backs up to a beautiful canyon. I preferred staying there.

I agree with Grandpere. You'll be able to see it in the distance shortly after you get on US14. There's a KOA at the entrance. Nothing else between there and Sundance.

I just pulled a 30ft TT with my truck (50ft. total) that way and its really not that bad. A few grades but nothing that should intimidate you. Devils Tower is impressive when you see it.

I would go US85 to I90 and then finish up with US14 and WY24.