Cut the plywood into 19" lengths 4' long, reinforcing with 2x4 attached with lag bolts. This leaves a few inches gap at the rear of the bed, necessary because I need to be able to reach into the bed to open the tailgate -- the outside handle doesn't currently work, and there are more interesting things to work on than fix that. Remaining to do for the first iteration, I need to upholster the deck panels with an old sheet, and trim the memory foam to fit (bonus, I can use the trimmings for pillows!)