As you can see Rip Van Winkle's floor does not have the top ply. This poor picture may help to describe what I an suggesting.
The top and bottom plies are inset into a rabbet top and bottom on all
4 sides then glued and screwed. Foam (in blue) can be added to insulate and add ridgity from racking corner to corner and some added support in the center.
I built Eggbert this way and with the removal of 4 bolts the body was removed in less than 4 minutes.