I used to be a basshead in my younger days. I learned the hard way.....my first couple cars ended up rattleboxes akin to your 80's buick that sound like the trunk is filled with coke cans. If it's big enough to interfere with the latch I'm assuming it's a largish ported box.....try going sealed and halving the volume, the mustang is small enough in the rear to generate enough cabin gain. I could help alot more if I knew the specifics. One of my side hobbies is DIY HI-FI. I've built my fair share of speakers/subs, both home and auto, and as a result I've educated myself pretty well in the subject. I'm not attempting to gloat.....just to help and be a resource.
2012 Kona Blue 3.7 MT82
Airaid CAI, Flowmaster A-back, BBK ceramic shorties, black enkei raijin 18x8.5, Steeda ultralites/pro action dampers, whiteline PHB & brace
RJW Aggressor matte black stripes, GT bumper/CS valance/Saleen grille, AM black shift knob
It is only rarely that one can see in a little boy the promise of a man, but one can almost always see in a little girl the threat of a woman. ~Alexandre Dumas