TSteeb

New to the site. Always had subs but nothing big. Looking for advice on building a new box for my trunk car.The sub is a obsidian 18 rebuilt by psi with lots of extra add ons. The box I'm currently running is a 5.3 cu slot port tuned to 30hzt sub up port back. Sounds good but trying to get louder. Thinking about firing into the cabin but because of the size of the sub I can't but it rite up to the back seat because it steps up in the trunk and isn't tall enough. Any help or advise on a box or how to run it would be appreciated.thank