Ideally, yes . . . but a car's truck is not an ideal setup in the first place. If you happen to have a trunk without loose panels, with good dampening material (most newer cars are equipped from the factory with such), a solid trunk latch that will prevent the trunk from rattling . . . That's pretty much what it boils down to, facing the sub towards the rear causes excessive vibratory noise from the car's paneling . . . On the other hand, if you face it towards the front, as close to the rear seat as possible, you still get the "channeling" effect - provided via the rear shaping of the vehicle. The waves that eminate from the rear of the driver will reflect back via the trunk, and those headed forwards will be channeled by the rear window. As well, the rear seats will absorb a good amount of excessive vibration . . . one needn't worry to much about such low frequencies being "absorbed" by materials, the waves will still pass right through and be quite strong in such close quarters. One aspect of all drivers many tend to overlook is that waves are traveling away from the driver in both directions. Sure, those headed rear-ward aren't as strong as those being directed by the cone, but they're still there . . . and in an enclosed space (like a car trunk) they've got to go somewhere. It also reduces the possibilities of noise cancellations (as loose panels, sheet metal, junk in the trunk, etc.) can start to produce their own vibrations as they're being vibrated by the waves. One could help things out a bit with a proper EQ adjust and properly adjusting the gain, but most seem to overlook such routes. Ideally as well, matching the size of the subs to the system is a good move too. I've never subscribed to the theory of over-loud subs. They should compliment the audio, not drown it out or be excessively noticeable.