you could sell the l7 to someone local with the box(some high school kid would love it), then get a good quality 12 or 15(FI, TC, Soundsplinter, etc) and build a box much smaller. For example, a Soundsplinter RL-p 15 can be in a ported box as small as 2.5 cubes, and you wouldn't believe the SQ difference.
If you are set on keeping it, try a little bit smaller box(i don't know what kicker requires), and you could try 3cubes sealed, or maybe 4 cubes ported around 30hz to try and even it out a little.