The design is convertible from a sitting arrangement, to a full bed. Basically it is two benches, with removable filler boards in the center. It had to be tall enough so that my cooler and water jug fit below, but still as short as possible to maximize the sitting space above. I also didn’t want seams in the mattress under my hips. Here is the rough sketch that I worked up to build the bed. The top is 3/4 inch plywood, and the framing is 2x3s. There were changes made along the way that are not shown here, most significantly a piece of 1/2 inch plywood on the bottom of the benches, and some simplifications to the framing.