Last November we took our 40' Diplomat including our Saturn Vue toad on a trip from San Francisco to a Thousand Trail Park located just outside Yosemite. (31191 Harden Flat Road, Groveland, CA 95321)
It can be done, but I have to admit that roads going up the mountain was very narrow in places and also very curvy. It's not for the faint hearted
but at slow speed and a steady hand at the stering we proved that it is possible. The difficult part took about a good half hour as I remember - the rest was OK.
Yes - we would do it again but it would not be a ride that I would look forward to.