This will be the first time I have built a ported box and I have a quick question. I am going to be using a round port. I was planning on using a 12" port but my dumb *** just realized that the depth of the box is going to be 12". I then figured using a 10" port and it looks like it will work ok. The question is how far from the back of the box should I allow for clearance? Also, any tips on mounting the port??