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...
Just a thought on the barn, you could eliminate the overhead door and install a sliding door. You could gain a foot or more in hieght if it works. Maybe not as convenient but it may work as I can only speculate without looking.