I have the following:
Upgraded battery up front, huge battery in trunk.
2 gua and 1/0 runs from front to back
Big 3 with 1/0 as well as additional 2gua grounds all over engine compartment to chassis, alt etc.
Stock alternator
Audioque 1200d at 4ohms (for now)
Phoenix Gold M-50

I was going to use both the 2gua and 1/0 runs for +12V between batteries, using the chassis as a common ground but after some reading I'm wondering if I wouldn't get more benefit from using one of the runs as a neg/ground between batteries??

Also, when doing runs between F/R batts, do you fuse/circuit break within 18" of EACH of the batteries, or just one or the other?
Thoughts/opinions? Thanks!