As part of the conduit-routing process, I added new holes into the lower rear box. There are three holes. The leftmost is for the upper-rear-to-under-seat conduit; the center one is for the lower-rear-to-front most-positive cable, and the right one is for the front-to-rear most-negative (2 gauge) cable:
Here are the conduit ends in place:
And here is the assembly with cables and terminals in place. The terminals are fiberglass, designed for this purpose, and provide a convenient place to connect the cells as well as the charger:
Side note: I've known about step drills for a long time, but this is the first time I'd ever used one (seen in-place in the drill to the lower right). For drilling holes in 1/8" or less steel, it is fantastic - no more changing drill bits from 1/8 to 3/16 to 1/4 to 5/16 to 3/8 for every hole... it "just works" (with a liberal application of cutting oil to help).