I want to build a box where the back wall is slanted so it fits tighter against my seat backs. How would I add a front slot port to a box like this.

port at the top/bottom of the box?

You could also do a tube ported box instead of a slot ported. That is what I am doing for my next box, also going to cut up a few different lengths for different tunings

__________________
Deck: Pioneer DEH-P8600MP
Ipod Attachement: Pioneer CD-IB100 Ipod attachment hooked up to an 80GB iPod Video
Speakers: CDT CL-60CV's
4 Channel Amp: Kicker KX350.4
Subwoofer: Alpine SWR-1242D in a Custom Ported box, tuned to 32hz
Subwoofer Amp: Kenwood KAC-8152D
Wiring: 2AWG to subwoofer amp, 8awg to 4channel amp, seperate runs.
Oh God...