I use welding cable , you can get at Princess Auto or other places , yes too heavy is far better than too light . I run the ground back up to the trans mount .
Yes 00 cable. Welding cable is perfect when you can get it. It has finer strands and a larger concentration of
strands. This also means less resistance and/or voltage drop. Voltage drop is the biggest
problem with putting the battery in the trunk. The longer the run from the battery, the more voltage you will lose.
To combat the problem, you use the heaviest cable you can find and/or afford.