Another short day. Waited until it warmed up a bit and then put up Christmas lights. Probably only worked on the car for about 3 hours.
I finally decided on 1/0 for the battery cables. A hole was drilled in the front end plate for the waterproof strain relief.
A 3/8" heavy stainless steel nut was welded to the side of the box. A length of 3/8" brass all thread will be installed here and nutted on the inside. The negative battery cable will go to the stud, grounding the body. The outer stud will have a cable connecting it to the frame.
I still have to figure out how to attach the lid and then build it. As for now, the floor will need the extra panels put in and then the box can be installed.