Just to answer the original question.. you don't JUST rewire from the truck, but internally to the batteries as well.
A dual 6v system in a fwc can see as much as 50amps of charging from your alternator when discharged, with correctly sized wire.
The rest of the wiring is fine, fuse block, solar etc. None of that is affected by this.
With my 2006 Chevy LBZ and Rolls 225AH 6V AGM batteries I saw 90A charging off the alternator.
