Your install looks clean. The flex isimpressive too.
I think you may want to consider another woofer
with that size box. I modeled the MJ-18M in that enclosure,
and it's less than optimal.
I think 2 Dayton MKIII 15's in the same boxes modified for
15" woofers would absolutly stun you with the difference.
They offer the same impedance and power handling and price.
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=295-420
The Dayton is in Blue and the MJ in yellow. Notice that they intersect at
about 120Hz. Below 120Hz the Dayton will just rip your car apart.
I promise you will see the difference immediatly.
I did not go through this trouble to insult your install,
just to make a humble suggestion.