Seven years I had a building built 14" tall so I could get a larger RV at some point. I knew nothing about doors, floors and sidewalls, but I told the large building company what I wanted. Bottom line...
I'm a little bit lost on your problem and what you are actually asking for. Are you asking for suggestions on a new camper, (like make, model, etc), or are you asking advise on how to modify the RV building? If you are looking for advise on the camper, and if it has to fit inside the RV building, and this is your #1 primary concern, then would you provide the dimensions of the building, and is there space once inside the door to extract the sides? This would help a lot.