Just got subs and amp. Need to go in 3GS

So i got a couple of 12"s for christmas and a 2600 watt amp to power them. plenty of power for sure.

I was planning on building the box myself to save some loot and having a shop install the wiring and maybe some sound deadening material.

the clearance in the back is 15" on the 3GS in the trunk which would make it easy to make a box that height for 12s but I wondered if shaving a couple inches off the top would allow for better airflow back into the cabin for the subs.... if that matters.

I was wondering if anyone else has done a similar setup and what the cost of install on wiring and sound deadening was if they are willing to guestimate.


thanks!