Update:
I did build a Deathbox, but ended up building a sealed box with 2 chambers for my 2-10" Infinity 1040W's, bridged my Profile amp to 150x2 to power them, and am powering the Polk 6.5 coaxes up front off the Alpine. I have the Profile running on the preout as a sub out so i can control it's level independently to match the music.
I'm fairly impressed with the subs. Zero bass boost on the head unit or amp and with the sub out maxed they will overpower the fronts almost so having the level control is nice.
So, for $450+- it's a very nice setup for SQ with enough power to hit decent on my type of music.
I may build a new sealed box to match the trunk once I get time, right now it's just a 13.5x13.5x20.25 with the subs on the ends.