That is some serious sub action for a boxster. I have wondered how a sub mounted in the rear trunk sounds. What battery(s) are you running with the system? I also have a JL Audio sub, but it is a little 8" unit in the passenger footwell. Several other board members also use that sub, it does a suprisingly good job for its size.
I think its corner location in the footwell allows it to couple with 4 surfaces to augment its output, like placing a subwoofer in the corner of a listening room, you normally get another 6db or so output. I dont know if it would work in your application, but you may want to consider mounting your amps on the sides of the front trunk like I did (see my website link below). It may allow you to carry more stuff in the trunk without messing up the amps. Have fun,
Ed
