I have a single sub in a sealed enclosure facing forward via the pass-through in the rear seat. There is no rattle, and to me it sounds better than it facing the rear of the car.
In the near future, I will make a new box, but down-firing (sealed), and the opening only out into the cabin of the car via the pass-through.
I only have 250 watts to my 8 inch sub, but it is a JL 8W7. Sometimes I want more (500w 10w7/10w6), but it compliments my 4x5.25 mids very well, You cant tell that it is behind you, the lows fill the entire cabin.
I prefer SQ over SPL.
