Most prefabs are pretty high, in the high 30s, possibly even 40s. You'd probably be better off having one custom built or building your own. I'd stick to their recommendations and do at least a 2.5 cu ft net box tuned to 28 hz, if you want even more SQ, I'd do 2.75 net tuned to 25. Smallest box they recommend is a 2 net tuned to 32, which would sound really good as well.
once again thanx for the info..the box is 2.2cu yet i cant find what its tuned to..you say make my own and tune it but umm..lol how the hell do you do that....im new to this $h!t but wanna do it right..
Nah the only real mechanical problem with ported boxes occurs below the tuning frequencies. At frequencies below and fairly close to this the driver quickly loses the dampening affects of the mass of air moving back and forth in the port which is internally 180 degrees out of phase(moving the other way). These two rapidly begin to move in phase and as result you get some serious cone excursion from that driver, but since externally these two sources are acoustically out of phase you get very little output. That driver is still going like a madman tho which can result in mechanical damage.
This problem is easily solved with what is called a "subsonic" filter which is basically just a highpass filter that shuts off the bass a certain point below the tuning frequency. 1/3 octave below is usually a good starting point if you have an adjustable one.
The only really bad result from tuning too low I can think of is reduced power handling.
If the prospect of changing port lengths seems a little too daunting thats cool. A custom built box like Jonathan recommended will not cost that much more(don't forget shipping) and you have the added advantage of getting a near perfect fit in your vehicle.