Slanted ported box
 

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 :D