We saw a guy at Yellowstone camping in a converted box van - you know, like a delivery truck. I don't know who did the conversion, but he had windows
cut in the sides and the entire back opened up like a toy hauler with a ramp so that he could roll his wheelchair in and out. It looked simple, not too expensive and very easy to use. We thought it was an ingenious solution.
When we were shopping for the motorhome that we had quite a few years ago, we looked at a rig (maybe 32' or so) that had a modified entry door with a wheel chair lift. The bathroom had been customized to be wheelchair accessible. There was no door to it, just a pull around curtain and it contained a toilet with grab bars, sink and shower with a seat and grab bars. A very nice rig, but I imagine it was pricey.