In case it isn't obvious, the panel with the 2x4 cleat slides back and the mattress unfolds to make a double bed, with about 2' x 5' footwell remaining in front of the tailgate. The mattress was saved from an old hide-a-bed couch. I designed the system over a couple years of planning and adapted my idea to the 2016 bed. The front legs of the 2x4 slide rails sit just ahead of the front tie down eyes that stick out of the side of the bed near the front, so it can't slide towards the tailgate. The front half of the panel is screwed down to the slide rails so the whole thing stays in place. It all could be removed by pulling four 1" screws, but it's a bit of a hassle just getting those panels in place.
Ignore the stupid baling twine. That remains from a couple weeks ago when we hauled a new wood stove back from town.
And we bought a bunch of those heavy duty storage containers and planned the bed height so that they would fit