i have 2 12 gt120 jbl subs i only have 5.20 cubi feet to work with i can build a slot ported box but i want to try some thing more difficult to build... also i havent seen a mustange with a custom built bandpass enclosure
if you're going to go bandpass you should run the ports through the rear deck and into the cabin and seal off the trunk. That way all of your bass is in the cabin of the car and none wasted in the trunk