So ... over the last few days I finally built the sleeping platform in our pickup/topper (a couple ~half days, actually - with time out for other stuff).
It's basically a double bed that folds/slides back towards the cab to about half size leaving rear 2/3 of 8' bed wide open. We bought a bunch of industrial totes about 12" high and I built the platform 12.5" off the floor so they just slide underneath. That still leaves us with tolerable sitting height above even with the mattress, which was salvaged out of an old hide-a-bed.
We're hoping to get away after Labor Day for a couple nights to do some sightseeing in the Beartooth and Bighorn Mts