The rear decklid? I really hate the trunk noise, so I figured a ported/bandpassed through the rear deck would eliminate the issue. Has anyone done such a box, if so, pics, details?

 

Haven't done a custom box ported thru anything (I plan on picking up the 4080 box), but one thing that I recommend everyone to do is to remove the 6X9 subs on the rear deck and allow the air to push through from the trunk into the car. This way, you will avoid having your trunk rattle like crazy, and will probably increase the feel and possibly SPL with the subs playing into the car instead of shaking the car from the trunk. So no matter if you are using a box under the rear deck lid, or a 4080 box, I am sure using those 6X9 speaker locations for venting the trunk will help..

Just my .02

 

If you remove the speakers and the baffles from the rear trunk lid you'll also be introducing all the road noise from the uninsulated compartment aka the trunk. So if you want to do this, dynamat the pi$$ out of the trunk first to keep the muffler and tire noise out.

Otherwise, use the body of the car to carry the bass...it's omnidirectional and carries through solids better than air (simple physics). If you were to only vent into the cabin, the air still has nowhere to go - so in order for that design to work, you'd need to roll down your windows. How do I know? Had a dual 12 a/d/s setup in my m3. It ported into the cabin through the ski sock opening (custom mesh grill with black cloth). Totally stealth look. But you open the windows and all of a sudden the bass dropped a few octaves.

P