Depends. Where is the box and is there a dimension that is "less-limited"?
I had a single Sundown SA8v2 in a .5 cubic foot box with like a 4 foot 3" pvc pipe aeroport.
Oddly enough, that was my favorite-sounding setup //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif and got surprisingly loud in the two-seater car.
If you can use PVC to make an external port, that's your best option imo