Yong
subs are designed to play the best in one specific enclosure only while will sound good or average (even worse) in other enclosure. Even Kicker recommend for SQ in a sealed enclosure and i did follow the instruction and the size of the box, its a 1 cu. ft sealed for CVR 12". it does produce some nice SQ but not enough for me. Btw i didnt say its so good, it has its pro and con compared to sealed and i'm into the pro of it.
Km chew
like i said, how low is low. For me 30 hz is good but i opted for 33hz. For ported, the bigger the size, the sub will be more efficient. You can have a 400w subs place in a 4 cu. ft box ported which will only need like 200w to play loud. The question is how much boot space can you afford? i can recommend you a 6cu. ft. box tuned to 28hz, but will it fit you car?