Im guessing your question revolves more around how you would go about constructing such a box. The difficulity lies in knowing accurately what the box's internal volume is/will be, due to the irregular shape. You cant just multiply length * width * depth to get your internal volume. So most people build the box to the size/shape they want, already knowing approximately the size (so they know it will accommodate a single 10" sub, or a pair of 15's, or whatever), then measure the exact internal volume by using styrofoam popcorn placed into the box until its full, then is removed and measured to determine enclosure volume. You can then use this exact internal volume to calculate the proper port length necessary for your desired tuning. The rest is like said above.... a tube and some glue basically.