Well, it was an enclosure I had for a 10" subwoofer that I put a baffle on to run the 8. That enclosure was 12" high x 24" wide x 11" deep with a slot port .75" wide x 10.5" high x 15.5" long. Since that was in the trunk I wasn't as concerned about a larger port area.
I have a smaller enclosure designed up for a single 1508 to use in my wife's 2011 Genesis coupe. I am planning on building it 10" high x 25" wide x 10" deep and using a 3" aeroport 16" long out the side of the enclosure. I am going to experiment with loading the port off of a wheel well and firing the sub into the rear seat and rearward with/without the rear seatback down to see what performs the best in her vehicle. I still may change this to a slot port just to make the build go quicker!