on my e46 with harmon kardon we used a small 10" in port tuned with a smaller punch pro amp (old skool 25x2 bridged mono = 196 watts rms cheater amp). the box didnt' take up much space at all and it pounded.
What i find odd is this logic 7 says it has subs up front but i don't feel any bass.
really weak. the e46 harmon kardon dsp on with a 10" in the back seemed to sound cleaner and definitely hit harder without being boomy. I just ran off the rear line inputs to the amp with a converter and ran a line level siginal detector for remote and a fused power to battery in the trunk. You could probably fit all of this in the spare tire area but you want the sub to aim towards the back of the trunk.