I dont have any more pics of how its secured to the box, but the picture right before showing the electrics, is where you'll best see how I did it. I think I also put a brief description of how.
If not: I made a section of strong eglass covered 3/4" ply going down the sides of the bed following the curves of the bed as closely as possible. They are secured via four grade 10 bolts into the truck bed original tie down points. Those in turn are bolted to the six side wing supports which are bolted into the vertical supports. The back of the verticals support (the one with the big circular holes at the back of the bed) is also bolted to the supports going down the sides of the bed. The side supports provide a platform for the hatches to rest on and be secured to, as well as providing the backbone to secure the whole framework to the bed without having any attachment to the bottom of the bed. It works very, very well and is extremely strong.
SCTracker, good question. I would say no. Why? The weight factor. If you will always have two people to remove it, great. But when you're on your own, the torsion box is easy to remove because its light. And damn strong. And if you make it 1" thick, it will be stronger than a straight piece of 3/4" ply, no matter what the quality really.
After much research I decided not to buy marine ply because its unnecessary for this kind of task (if you have it under a topper). You're going to seal it somehow and that will help the waterproof factor. 13 ply marine grade wood sure sounds good and the extra ply is awesome, but a torsion box seems to tick the boxes better. My suggestion would be something simple like a nice 1/4" sheet, with 3/4" "verticals", and then another 1/4" skin on the other side. Strong as hell, light to boot. Use a good wood glue to secure the verticals to the skins, and you'll have a very very strong platform - easy to make to boot! (it just looks hard - well, it did to me. But in reality... its simple)
And as always, thanks everyone for your kind words.