If you happen to be driving along highway 16, there are 4 tunnels pointed straight at the monument. Stop at the second or third one. THe fourth one is always crowded as it is the first one from the other direction, and most do not know about all 4 tunnels.
Also as you leave the monument parking lot, turn to the right, go about 1/4 mile, and there is a small parking area, you can get a side shot of Washington from there.
I stayed at Custer State Park, and it was a few miles drive to the Mt Rushmore parking area. I guess I did not want to take my RV that close to the monument, when I was going to be leaving and going toward Denver CO.
On another trip, I stopped at the 'little house on the prairie. It is in DeSmet SD. Not to far from I90. There is a small campground right on the old homestead visitors center. Laura and Almonzo Wilder's homestead is not to far north of there.
Interesting little town. Still has the Rail Road going through town, and a large tractor dealership there.
Have fun camping!
Fred.