18" audioque in hatch box design help!

[John Skipper]

I have a 93 mazda mx3 im looking to put a audioque hd3 18 on a hifonics brutus (this years) brz1700.1d

MAX Dem's are

30 wide x 24 deep/back and x 20 tall or up and down

thats max i want to keep it 5-6 cubs 30-34 or 35 hz tuned with the 80-100 for port volume...

not a great box designer best port i could get for that was 4 inches x15.5 back and 8 across for a l port

not a big fan of l ports but icouldnt get it tuned low with out so any ideas or tips would help greatly