There are many sources for Handicap Accessable RVs. Just make some Google searches and you will find used ones for sale and also companies that modify or build units for just about every need. Most of the RVs are larger ones so there is more room inside.
2009 GMC Sierra XLT CrewCab 5.3 4X4 w/Runningboard lift
2009 Viewfinder V21FB w/ Handicap Assists