Searching for right RV for cross country with disabled son.

There are a couple of things to keep in mind for wheelchair access.

First off, the height of the vehicle door off the ground. If you get one that is too high, you may be beyond the use of many portable ramps. There is a great resource here for determining the correct length ramp for the height of the door you are using it at: Wheelchair Ramp Wizard

The other consideration is the width of the door. Most RV's have fairly narrow doors. Most portable wheelchair ramps are made to 30 inches wide, so to use a standard portable ramp, you would want to find a unit that has a door that opens at least 30 inches wide. If so, then you should be able to use standard Wheelchair Ramps like these.