I perfer round ports as opposed to slot ports because it minimizes surface area (what creates port noise) to port area. As for the box, if you don't want to tune lower, you don't have to. I like a 15-16hz tune mostly because it gives the driver a bit more protection from unloading. Honestly though, what's the difference between 16 and 17hz? If you want a 13ft box tuned to 17 hz, do it! It'll rock.