I haven't run it yet, but since I'm planning on moving the battery back there, I figured 0ga would be fine. Since I hate both of my jobs so much, I had plenty of time to consider different layouts and set ups using different wires and connectors. I think I'll go with the thicker cable.
But, I did come up with a really good idea; our chassis could act as the conductor! Ok, hear me out-the driver's side frame rail is + and the passenger side is -, all you need to do is isolate the rails and you're all set! I think that'd be about -20ga!