Front battery Toolmaker terminals from CJ18
A whole lot of 2.5 by .75 inch mdf strips to add more strength to the rear wall.
Once these are in place brings the rear wall up to 4inches thick.
Still need to put another 3/4 inch sheet over these yet, and at least 2 more layers in the back which should make it 6.25 inches thick, may go for 7inches, gotta be sure to leave room for batteries however.