It is pretty simple to make a collapsible solar box cooker from two cardboard boxes. The trick is to cut off the bottom of each box, creating two pieces: the base; and the sides. After that, it is possible to collapse the box by folding up its sides and laying them into the base; or, when you want to use the cooker, insert the sides right into the base, extend the accordion sides, and fold the flaps down inside.
The lid fits perfectly onto the base of the larger box, so that, when collapsed, the cooker takes the form of a convenient, briefcase-size box. Links to construction plans for this cooker are found below.