well if your leaving the seats in.. what subs are you going to use to use that will handle 4K? and what alternator/ alternators do you plan to run? 4K on a single alt you will need more then 4 batts. i have my wires ran under the truck as it was easier that way rather then under the carpet for me. how many runs do you plan? i would shoot for at least 3 of each. and if your using batts in the rear, just ground straight to the batteries. what amp are you going to use?