depending on the deminsions of the box and placement fo your soon-to-be port(s), you shouldn't have much of a problem. seeing that you have a pair of 12's, i'd would go with two 4" ports. the cut out for them, i believe, is about 5-5 1/2". if you decide to go with two ports, you will need to make them longer than if you only had one. like i said before, the length (or going with 1 or 2) will depend on placement and depth of your box. they do recommend the flar edge to be as far away from the box wall as the port is wide, in the case 4" from the box wall, i have put them closer with no problems, and you need to keep the back end at least 4" from the back of the box. when installing them, they also come with their own formula to cut them to lenght...due to the flared end coming into factor. if you look on partexpress.com they have "precision ports" for a good price. if you need any more help, lmk.