Looking at your route, you maybe better served by taking I-90 to the north side of the Black Hills and staying in Spearfish. Chris's Camp is a nice place, great owners, easy on/off the interstate.
Spend two nights, take a day trip down HY 385. 385 to Keystone/ Mt Rushmore, then 16A(Iron Mountain Road) great winding road thru the hills with nice views of the Presidents. 16A to Playhouse Road(753) to 87(Needles Road, a must do) up thru Sylvan Lake to 385. 385 back thru Deadwood and back to Spearfish.If you want to see the Crazy Horse Memorial go south on 385 about 10 miles from the intersection of 385 and 87. About 170 mile trip, easy 1 day drive.
Great day trip with no 5th wheel. 16A and needles are best done with just the TV. Keystone is a nice tourist town. Deadwood has casinos with good eatery's. Go see Boot Hill and a few other things.
When you leave you may want to go to ND by of US 85 to Belfield and then 94 east. Better, faster road, less intersections and stop signs, and a town, Bowman, then the route are planning. It is about a hundred miles from Belle Fourche to Bowman. Longest stretch without a town.
If you have time stop by Devils Tower, adds 25 miles to your trip but well worth it. There is a KOA there and a National Park campground (no hookups) but nice for a night.
Have a good trip it is a nice area, but make campground reservations.