Help with box for 2 12" Icons

[tysonm]

My dad is going to help me build the enclosure with his CNC machine so things should go smoothly when cutting the boards to their correct lengths. Right now I have a 2.3cu. box tuned @ 33hz (which I built it myself) and it gets decently loud, but I want to get louder which is why I decided to make an enclosure which will hold two Icons.

I listen to a variety of music such as heavy metal, alternative, rock, R&B, rap, techno, and some dub step. What type of box will be the best to build to achieve this?

For an enclosure to fill up my trunk completely (2011 Mazda 3 Sedan) it would have to be 30" Deep x 37.5" Wide x 15.5" Tall.

On a side note, I also wanted to do a Kerfed Slot Port. I'm not sure if this will affect the type of box to build or not.