port directly into cab

im thinking of building an enclosure that has the subs firing upwards and has the port firing directly into the cab of my car. (almost like a walled port) it would be butted up against the backseat and the backseat would be folded down. there is an opening when the seats are down that is 12.5" high and 26" wide. is there any downfall to having that kind of setup VS a rear firing port that allows air to pass over the enclosure and into the cab?

Use the pull down rear seat to open up to the trunk, sure, but port into the same trunk cavity that the woofers fire into. Woofers can fire upwards, port fires to the rear...woofers to the rear, port upwards...both in same direction... As long as everything fires into the same void. The pull down seat just opens the cab up to the trunk a bit better.Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

thank you very much! im goin for SPL and am trying to get the most airspace as possible in a 2000 camry trunk, any suggestions?