[Peck]

a suggestion:

make the bottom be set up in some way so the sides can move in and out with enough range that you will always be able to fit the robot frame to that (the width of an industry standard door or just smaller would be a good idea) then have the top "rails" be set with holes and have pins that slide into the holes and stop at a certain height. That way, you can have it resting on the wheels if u need to and on the frame when u need to. If you do it right, new pins could be made in a madder of minutes on a lathe if you need taller or shorter.