I had a ported bandpass box I bought from Circuit City years ago.I put 2 10" Polk subs in.I had to do what StangGT did,take the back seat out.The box just "BARELY" fit through.I thought it was loud with my Alpine Amp.But compared to most sound systems,the bass loudness just never cut it.It was pretty low.And after I put the box in,the back 6x8's sounded like sh**.The subs couldn't breathe well..neither could the 6x8's because of the box taking up the air space.
I could never get any good loud bass out of this car.That's the only thing that sucks about Mustangs.No room for boom.