Pianottuna - If someone wants accurate knowledge of the charge state of their batteries and how much is being drawn by the equipment in the RV and wants to monitor recharging then a Trimetric or similar digital device is needed. These should be standard equipment in all RV's but they are not.
It needs to be shielded or twisted pair wire and I used 18ga alarm wire from Home Depot which has a foil wrap. The heavier gauge makes it easier to feed without damaging the wires though 24ga would work electrically just as well.
I ran the wires from the battery compartment behind a furnace and through an overhead cabinet to the panel area where my other meters are located. For a section of the run inside a cabinet I put the wires inside small diameter PVC pipe which was easier than cutting a piece of angled trim strip and mounting it inside the cabinet.
Length is not critical for the wiring run so you can go with the easiest routing and not the shortest one if that helps.
