does 2 #8 wires equal one # 6 or #4 for added battery

Great information guys thanks, based on further pondering of all the factors, I think I will just leave it with single #8...The 3 pin connector I am using between the truck and the TC will only accept no larger than #8 so that will always be an issue. I have yet to take a trip with the TC yet, so after a couple of runs If I have to upgrade then I will re-work it. And yes I am only looking to maintain the batt. for a full charge I can use a gennie and charger.