Series/parallel wiring completed. The outboard terminals nearest to the bus will be the main pos/neg terminals for the charging & load connections.

Weatherproof access box and 2" PVC conduit extending to bus interior. The conduit path is under the bumper, and then forward about a foot to arrive under the bed. The black cable is the pilot I'l use to pull the main wires through the conduit. (I'll use a smaller pilot once the big #2/0 wires have been pulled.)

Weatherproof access box, viewed from the inside of the battery enclosure.