They are made of 4 mm thick marine plywood or form plywood (I don't know the English name right, I come from Belgium). I make them from that material so that they are watertight. That's on the work sometimes necessary
Dimensions are; height 5.2 cm, width 10 cm, length 10 cm, 15 cm or 20 cm low model and height 10.4 cm, width 10 cm, length 10 cm, 15 cm or 20 cm high model.
They are going to be used as stokage in the truck.