Here's the tension rod we used.
I can't remember the dimensions exactly and my sketches and notes are at home. I know it's about 46.5" wide and I'm 6'3" tall and can lay down completely in the fully-extended platform. I'll get exact dimensions tonight and update the post. I might even include my sketches, too.
That was the goal! We ended up taking the third-row seats out semi-permanently. We kept them folded down since we bought the van anyway and the extra cargo is nice. We are keeping them so we can put them back if we need the human cargo space, but that's highly unlikely for us. The bottom line is that we wanted to keep the full passenger functionality while being able to use it as a mini-camper, too.
Nothing is holding the reflectix except for the second-row windows (sometimes). I cut the pieces to a size that would slot into the window and fit snug. When we have the windows open and the tops of the second-row reflectix folded down for ventilation, they don't stay, so I keep four shims to hold the front and have some small velcro strips to hold the back. This last weekend, we camped with our dogs and the reflectix stayed in the whole time without a problem.
I'll have another update with the dog adaptations that I built/am building when they're finished, but here's a preview of a second-row removed platform so our pups have a place to be that's safe for their paws while we travel: