ABOUT THIS PHOTO:
One of the plywood boxes occupies the "wing," the section of floor between the main plywood panels and the car's sliding side door. Here the wing is partially supported by three legs that stand on the plastic door runner. A later method of supporting the wing eliminated the three legs.

ABOUT SYSTEM 5:
My fifth and current system involves sleeping atop a set of plywood boxes having detachable lids. In the Summer of 2010 I built ten plywood boxes of various sizes to hold travel gear. They replace the Rubbermaid totes I had used for years. This system eliminates the need to move things because the boxes stay in place throughout a trip. It also eliminates the plywood-handling nightmare of the previous system---the lids are small enough to be easily handled and stay with the boxes.