Must be vented. I see no reason for a small gauge negative cable, except it has less length. No manufacturers I know of shut the poistive power off with a solenoid. Use the bggest cable you can get . Welding cable works well. The area behind the trunk at the back seat should be sealed with metal . NHRArequires a rear accessible shut off switch in the positive circuit. Though street use not necesary. NHRA also requires 3/8" battery hold downs. Dont forget to reinforce the floor area under the holddowns.
Doug