My Class C is about 24 feet and we always drive with no toad. It's been all over the western states with no trouble. Big problem at Mount Rushmore is paying the fee for parking the parking structure that looks like it was designed for the downtown of a large city.
If there is a big problem with length or height, there will be signs for you. In some areas on the east side of Yosimete, there are signs for state highways that say the limit is 21 feet -- and I once had to back my older 21-footer up to make a curve.
Just enjoy yourself - and remember that even at automatic transmission can be shifted down for extra control on steep areas. Also if it scares you just slow down. That way you will do less damage if you do hit something.