My newest box design with 3d image

first off, carpeting the inside of a port will not change the sound, carpet is not a solid object, sound can go through it and it does not take up hardly any space so it's not going to change tihe dimension of your port,

second, what frequency are you tuning your ports to?? if you tune it to low you'll blow you subs apart. different subs can handle different frequencies, the rockford stage1's are the lowest rockford model and they don' t sound that great vented, why don't you go sealed.  i sell rockford so i am very familiar with their capabilities.  and instead of 2 8's why not 1 10.  you could probably get 1 10 stage  for about the same price as 2 stage1 8's  if not cheaper. 

third, slotted ports, round ports, and square ports all have the same output, there is not one better than the other it just depends you box size and tuning frequency. 

also if anyone needs any boxes built, you can send me the specs that they need to be and i can built it and ship it.  price would be material x 2 + shipping and handling.  MDF is not very expensive so you're not looking at a lot of money, a box for 2 12's would probably cost you around $50