Hey so i have a 98 grand prix gtp and need it to be as loud as possbale i currently have a 2011 AB VFl 18" and a AB 450.1 on its way so no worries in the power department. Now my question is i want to build the best possble box for this sub/car i have a ski hole thats 12 inches across and about 20-24 inches high *the rear seats do not fold down*. I also have 6x9 holes in the back and right beside thows i have 3" holes as well. Now i was thinking i would port threw the rear deck but not to sure what results i will get with that. But when i was testing i got a gain of about 3-4 db when i took my 6x9's out. My car like 44 hz so that what the box will be tuned to . Just throw out some ideas i need a second opinion on all of this. if needed i will upload some pics. thanx a bunch!

 

have you considered swapping out your rear seats for a newer gen pair that do fold down? (and trimming the metal to make it work) I have a buddy who is in the process of doing this now,(his is a 01' though)
and yes 6x9's out almost always make a difference in these cars.
Look up Thorshammer1508(I think its 1508) on youtube, he has a similar car(just a grand prix iirc) but he was quite successful in getting loud, but a ton of batteries to back up everything.

 

it is not possbale because my seats are leather and the new gen seats wont work for me.