Re: to rear fire or not to rear fire...
It possibly could be louder, I'm assuming you are firing it off of the back wall of the cab? That wall would have to be sound deadened, and then i coudln't really see a reason why it woudln't atlesat be the same volume, maybe a little more. I know that in home theatre for maximum spl you should put your sub in the corner of a room because it will allow it to reflect off of the most walls. Also many people including myself have had more luck firing subs towards the back of their cars. But it is heavily dependant on the vehicle. I say go for it.
Alpine CDA-7995, A/D/S 3 Series Comps, ED 8A, SoundStream Reference 604, 98 Civic Sedan