Originally posted by SiClone
I good ported box would definitely increase the SPL inside and outside of the car. But the ported box would also be bigger than the sealed box, so are you willing to lose more trunk space???
But before you get to all of this, maybe you should look into different subs. XLC's are old and weren't exactly Rockford's top subs back then.... I'd suggest a single Kicker 15L7 in a 4.5-6 ft^3 ported box.... 
Thanks Si,
Appreciate the input, man....I sure am going to look into new subs; that was gonna be my next inquiry----I know these XLC's were Rockford's middle ground model, but I wasnt sure if they were the culprit of the ineffective bass....I should have gone with Kicker in the first place---I had their SS12 box years ago and it was a BEAST---I loved it. Kicker is definitely my first choice for new subs; how about two Kicker 15" L7s? Could my Rockford 800.2 power these efficiently in bridged mode? This thing puts out about 800 watts RMS mono; could it kick the Kickers good enough?
And do you think with a ported box and these Kickers, the bass will be definitely heavier in carrying outside of the vehicle?