Vent or no Vent

it'll depend on whether the sub is a free-air sub or not..

Strictly speaking sealed enclosure type subs need the pressure created by the cabinet to prevent the cone from travelling to far, and to "suck" the cone back in.

However, those that know what their doing can add holes to an enclosure, or "port" it, to tune the bass characteristics of the speaker. Porting will usually extend the frequency range of the speaker a little, but the trade-off is that you'll lose the punchiness and won't be able to drive it as hard. The idea being that the less pressure of the enclosure, the longer throw of the speaker. The plus side is that you'll get a smoother, deeper, rolling bass.

It all depends on what music your going to be listening to, and how tight you require your bass to be.

Most subs can be fitted in a sealed or ported enclosure, but the enclosure has to be designed correctly to accomodate a port. i.e. you can't just drill a big hole in a sealed enclosure and expect it to work. The port has to have a calculated distance between the back of the cone and the port, in order to avoid cancellation i.e. the air from the rear of the speaker cancelling the air from the front.
Ported enclosures are generally more efficient i.e. you'll get more out with less power, but are larger and can also be tuned to provide boost at certain frequencies.

if in doubt some sure someone (like me) could knock you up a design, and even make the box if needs be