Thanks, Windguy
The extension is actually where our feet/legs go. It's the shorter section and narrower, so it is plenty rigid and you can get your legs down on the side, step on the sliding door sill, pull the inside door handle, and you're out. It also means my wife and I don't have to climb over each other to get in and out.
Good 3/4" hardwood ply and climbing rope on each corner holds a person's weight just fine (I'm 180 lbs and my wife's a lot lighter). I skipped the leg option on the extension because I found I didn't need to add the complication, especially with the milk crate in the center. The ropes also allow you to lift up the bottom part of the bed part-way and keep it there by hanging the loops on the bolted in hooks just above the sliding doors. Then you have easy, hands-free access to anything underneath. I can also fold the whole thing back up and reinstall the rear bench seat to make the TC a functional wagon. The bed and back seats can coexist, although I took them out for more storage space while camping.
Next up is pulling the headliner and insulating the ceiling as well as contemplating a roof vent. I'll start a new topic/thread in the "modifications" section if you or anybody else is interested in more details/pictures.