O.k, I'm just going to assume a couple of things so that I can try to help, let me know if I'm assuming wrong...I looked at your sub online...
http://www.lightningaudio.com/produc...en_US&p_status=
you have a few options,
ported - (replace the ports after you get the box in the car)
sealed - (buy a new box), (rebuild another box out of the old one)
............(make a false bulkhead w/some cleats and another panel)
if you decide to keep that box and you continue to use it sealed, I'm assuming the box is built to "ported"
specs...you do not want to invert the sub, you're trying to get rid of space...inverting it will only do the
opposite...you also have a higher chance of mechanically overstressing your sub in a box that's too big