hi, im making a sealed box right now for my 10 in. subs. now thw box is around .7cu.ft for each sub individually. now if i want to try and make a ported box for those same subs, its my frist time so im not sure, how will i know how much bigger to make the box? people said you need a bigger box for ported. also, since my subs will be facing the rear i will go with a slot port place beside the sub facing the rear as well. so since a have 4 10's , all facing the rear, should i just put only one long port or do i need 2?? thanks