Rear Walls
In the space between the 8x8 poles of the interior racks I glued some 4x8's to the rear wall. I then followed that with some small 4x8's horizontal boards to complete the wall framing.
(total pieces of wood: 374)

The rear wall has been covered using the same 2x6's that were used on the side walls.
(total pieces of wood: 451)