If you were to remove just the flat portion of the rear end, the window and the panel below it, you would have something that possibly could be reversed later on, and the fold-down would be a flat piece. The problem is that you would have only about 40" wide by however high your top of window is, to roll your bike in. Otherwise you are getting into the curved wall sections and endcaps, which complicates things quite a bit.
I would also be concerned with the useable space left for sleeping and such with a small Airstream like a Globetrotter. For long-term comfort and useability I would go for a Safari(22') or Overlander(24 or 25'?) at the very least.
Rich the Viking