If you want to stay with a Class C, look for used Born Free mobility units. Before they closed their doors this year, they built several custom units for wheelchair & power chair users.
DW is a quad from polio, and uses a 3 wheel scooter with a seat lift full-time (indoors & out). Our current lift van couldn't be towed 4 wheels down, so we wanted a medium sized C without a tow vehicle.
You can see our floor plan as "Mobility RV 3" @
Born Free Mobility RV's.
The key to our shorter unit is the mounting of the wheelchair lift on the back door, rather than the more normal curb-side mount. We selected a Ricon lift that splits the platform when retracted, leaving the rear doors usable for "walkers" on the Kwikee retractable steps. That required us to go from 24' to 26' long, but gave us space to store 2 folding DecPac fiberglass ramps (1 & 2 meters long) and DW's backup folding travel scooter. (When a scooter is your legs, you can't go on a cross-country trip without a back-up plan!)
One advantage of the Born Free units is their steel roll-cage, that has been approved by Hoyer as suitable for ceiling mounts. Because she could slide transfer, however, we used a B&D Independence power transfer seat base with a 180 degree rotation to go between the passenger seat, her scooter, and the drop leaf dinette. We also retained the Born Free design for a wet bath (since she couldn't stand for a shower -- and since most campgrounds might have an "ADA" toilet but rarely an "ADA" shower), but added a Big John expanded toilet seat for easier transfer.
Even our sofa is a queen-sized convertible bed, with an air-over-springs mattress to adjusting for "downhill" transfer to/from the scooter seat, using a slide transfer board. DW's scooter would stay in the kitchen aisle next to the bed, and I had a urinal for my new nighttime excursions, so as not to crawl over until morning.
DW is a retired Vocational Rehabilitation counselor, so we knew what adaptable products were on the market. PM us if you have further questions.
Final warning/tip: with a Class C modified for disability, you better be comfortable with living in smaller spaces and work out signals for how/when to pass each other in the passage.
(Because of health issues, we're no longer actively on the road, and will probably have to put our 2010 coach on the market.)