since it is so very hard to find a place that sells 3" subwoofer ports for my mod....i decided to make some (i need 2)....i will probably use pvc pipe. but i dont konw how to make that little lip at the end. Here are some pics of a 3" subwoofer port.(3" because that would fit a 80mm fan perfect.)
(located on the side of the box in this pic)