The whole job · 2:14A box, and a lid made to fit it
A box 80 by 60 by 40 is hollowed with a center rectangle pushed down 37, leaving walls and a floor 3 thick. The lid is drawn on the box's own rim, its two corners snapped to the box's corners, and pulled up 3 as a part of its own. A lip 0.2 smaller each side than the hollow is drawn on the lid's top and pushed down through it. The eyes in the Parts tab hide each part in turn to show the lip and the hollow.
Watch the whole job

