i'm not to familiar with sub enclosures, but is it that expensive to make a custom fit box to fit into one of the sides? i used to have 2 12 inch subs in the back of my previous 2005 TL. it took up SO much room. i'll never do that again. custom boxes w/ a single 10 inch W7 and a good amount of juice... yum!

OP - did your installer have any issues integrating the woofer into the factory deck? did he unplug the OE sub in the back or is it still on?

 

I had mounted an amp directly to a box and had no issues in 10+ years. I agree that it isn't ideal, but sometimes it is the best/easiest solution.

Also, I agree with zoop425 that sealed boxes are the way to go. While maybe not quite as high of spl, the sound is much cleaner.

 

big fan of the intake

not so much of the trunk setup youve got going on there.