Kicker solobaric are good for tight spaces. Afreeair sub is designed for a huge box like a trunk...they still have to be sealed off..this is kind of decptive. I used to think you could just mount them to a board and they would be fine, not so. Or if you are buying a sub get one that requires the lease amount of space for a sealed enclosure and fill the area behind the speaker with poly fill
Brent