Winnebago makes two accessible motorhomes. They can build you one with a lift, the Inspire, a diesel Class A, or the Roam, a gas camper van on a Ram chassis. Both are designed for the wheelchair handicapped. Check them out and check with Winnebago to see if they still build custom coaches for special needs. Then please come back and educate the rest of us.
The previous owner of my class A put in half steps for is wife. He was a retired doctor. After several years, his wife finally could not do the half steps. He made them out of plastic leveling blocks that could be removed with ease. He use a plywood base. I don't know if that would help you.
This just in: June issue of FMCA's magazine "Family RVing" has an article about accessible RVs. It mentions www.handicappedtravelclub.com for information and encouragement to travelers with a wide range of disabilities. The article may not be of value to you, but the group may be a big help to you.
If all else fails, read the directions!!