If you have a three-way refrigerator that runs on 12V
, there are two separate runs reguired. For the first run to the control board 12 guage is fine. For the power supply connection 8 guage is suggested. For the connection between the charger/converter and the house batteries you may want to consider a heavier connection. I used 4 guage welding wire, which is very flexible and should assist with robust charging.
The battery side is a whole project by itself. There is a battery disconnect, a battery separator and a battery isolator, all of which do different but important things. Might suggest discussing your needs with Randy at Bestconverter.com if you don't have a clear roadmap in mind.