I run my Type R 15 in 2.5 cubes sealed. That's about the biggest you can go with the 15. It's also in a Grand Cherokee. Other than the resonant frequency of my vehicle being high, the sub sounds good. Out of the 4 different subs I've had in there, none have really been able to play the lows too well... I'm blaming the resonant frequency of the Jeep for that one.