Upper Pines (and probably Lower Pines and North Pines) have handicap sites. The valley also has a ADA compliant shuttle service that runs between the campgrounds, Happy Isles, Mirror Lake Trail head, Curry Village, Yosemite Village, the Ahwanhee Hotel, Yosemite Falls, Yosemite Lodge and Housekeeping. (Oh, is it good to call these by their original names!) There is paved roadway up to Mirror Lake, but I'm not sure a rig your size would be able to turn around. There is a tour of the lower valley that is in an open, adult size kiddie train sort of set up. It takes you past some of the rock formations with a park service guide explaining what you are seeing. I believe that tour leaves from the Yosemite Lodge, where there is a shuttle drop off or parking. I've never been on that, but I have seen/done all of the others.
Other places with short walks are the Wawona Hotel and Pioneer Museum on the way into the valley from Oakhurst. There are several museums and galleries in the valley itself. It is a long ride from the valley to Glacier Point, but in the summer it is spectacular. Not too long a walk to the Valley View.
Bears haven't been a problem for us (I go every spring with a group of high school students) for several years. You have to be careful with your food and obey the rules, but I haven't seen a bear in the campgrounds for a long time.
Here is a website concerning accessibility access in Yosemite:
Good luck and have fun!