designing enclosure for inverted 15

I picked up a Lighting Audio Strike Series S4.15.VC2 for a REALLY good price, but the box the guy had it in was too big for my trunk. The only way I could get it in was to cut the ports that he had extending out of the box and plug them, leaving me with an oversized sealed box. How would I go about designing a box to mount this thing inverted, so the actual enclosure can be a bit smaller?

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/products/product_details.asp?cat_id=2&series_id=19&family_id=27&item_id=94731&locale=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

really depends on just how much bigger the box is than it should be.

The box fits perfectly in the trunk, the problem is the trunk opening. I'm gonna try to rip the ports out and replace em.

the last car that box was installed in probably had the ports coming through the back dash...

that can actually be a good way to "funnel" the sound in from the trunk

Actually, it was in a scion xB. How am I supposed to get the ports of the box to replace them lol?

sometimes people extend the ports outside of the box to get the tuning frequency they want....
long ports could be compensated for with slots, corners and curves...

ports outside the box are usually "fart boxes" ..... they are small boxes with a high tuning freq, made specifically to play a very small band of freq's (around 50 Hz or so) very loud.