Thanks for the info.
Use that as a guide then a loss calc to determine.
Also price wires because they're expensive
Mines a 40ft DP prevost with engine in back and 12v under front bumper. The alt wire was oem so I'm betting 2/0 and needs to be 4/0 so luckily with a wakespeed I can just plug usb into the app on a laptop and turn it down.