Thanks to the great people, Jessica, Kobus & Jared, at www.liferemotely.com who supplied pictures and info on the mods they did to their own 4Runner, I was able to get a base plan together. I started by attaching 17" tall x 1" thick boards to the frame with corner brackets to serve as the base for the back "shelf".
I pulled the carpet and padding up for this, as you can see. Here is a shot with all 3 boards in place and the carpet laid back in place:
Next came building the back foldable/removable shelf. It is 3/4" plywood, cut into 4 pieces and attached back together by door hinges.
Now for the magic of cheap, low-quality carpet! I also added and carpeted two thinner supports (one you can see on the left) on the sides.
Now watch it fold...it can fold in the middle too so that I can just fold up just one side.
Now the view from the inside. This shot shows a carpeted lock box with a carpeted wooden block standing on top, which serves as the support for the front shelf. The block also hides the already-hard-to-see key hole for the lock box. To the left of the lock box is one more standing support board which stands just about 3" behind the one supporting the back shelf.
Kuni, let's see what's in the box! Nothing! Absolutely nothing! For anyone that has never seen UHF from the 80's, it's a winner. In reality, this box with hold my most valuable possessions.
I am going to keep the back seats down as much as I can so that everything will be hidden from view, but I am happy to pick up fellow travelers so the back seats do function as normal still.