if you have the battery in the rear you must have a cutoff switch at the rear of the car to run down the track legally, and the purpose is so they can shut off the car. So it has to be wired thru the altenator also. Its alot easier to pop a hood in a wreck than a trunk.
NHRA rules makes you use a shut off swtich and tim is correct it has to go hrough the altinator other wise it won't shut off. And the box has to be sealed from the drivers compartment, which your rear seat I was told would work as that. Normal batteries need a box, optimas or dry cell bateries only require a hold down, they dont need a vented box as others do.