vented is easier then you think,
usually subs tolerate about 0.3 cuf above the reccomended factory spec.
they state that this includes the basket but i usually make my boxes about .1 to .2 cuf bigger then this rating.
the only thing you really need to be concerned about is tuning. port diameter and port lengeth determin which frequency your box will sound the best or loudest at.

the12volt.com has some good box calcs and some nice port calculators for you disposal.

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