To the OP ... Ron Dittmer's advice above is absolutely right on the money!
If you want to visit certain large U.S. cities then merely camp outside them and rent a car to make day trips into and around any particular city. Otherwise, renting a small RV to visit the rest of the U.S. is a great way to go.
By the way, we have lived in California for decades (my wife is a native), and many parts of this state are of course spectacular to RV camp in. We stay away from populated areas in every state when on RV trips in our 24 foot Class C RV, and have made 9 week and 10 week RV trips across the U.S.. They were wonderful experiences that never could have been duplicated in using a car and motels.