Minimal, I am methodically going through this process as well. We are going lithium and I currently have the Anderson connectors in place, with one mounted into my back bumper. This accepts a short pigtail from the camper batteries. This allows us to have 4-6v AGM batteries in series/parallel.
I'm researching the DC to DC charger now and will run 2 or 4 gauge wires from the truck battery to the Anderson plug in my bumper with the necessary fuses in place. I think I'll run another lighter gauge 2-way from a spare upfitter switch in the dash to activate the charger in lieu of another ignition source.
