My buddys excelon was doing that last night we re wired all his speaker wires to his mids/high amp and it still did it. We turned the bass down on his crossover for his mids/highs (which was like 1/4 way up) it then played fine from there.
Possibly 3 15" AQ sd2.5? Theyll get loud as hell and still sound fine(unless your an audiophile) those subs are on sale right now too
Edit: and is your electrical up to par with all that? Like a H/O alt or alts, multiple agm batteries, big 3, ect.
Awesome gorilla tape and cardboard i guess great minds think alike. Works great for me but for the air leak i would also recommend gorilla tape like mentioned above or expand foam
Edit_ whoops just noticed this was an update. Thats good to hear that it worked for ya, did u use gorilla tape?
I put a little over 2500rms to my hdc3s i have 2 12s and im tuned to 31hz i run at full tilt everytime im on the e way i run them at full tilt for hours everyday(yes im always on the go). I am hard on subs and ive had these for over 6 months w/o 1 issue w/them i am verrrry pleased. im happy if my subs last a month lol (not joking) these subs impressed me expecially with everyone who tried an talking me out of buying them, saying the suspension would break or they dont like low tuning ect. Well they are loud and low i can play 20hz tuned to 31hz and i didnt loose the punchy notes or higher freq. Im on mobile or i would post some vids(unless someone knows how to post em mobile). I say go for it its deff worth it