I put a lot of work into my rear deck to get it not to rattle and it still buzzes slightly. Definitely not enough to get back there and mess with it again, but when my 12" with 750 watts RMS hits hard, there is a slight buzz. I can live with it.
The Wicked Audio enclosure really doesn't take up much room in the trunk. It fills the space of the trunk that is barely used for anything anyway.