Joe Black:
Volume estimate: 0.7-0.8 cubic feet by my calculations.
If you are going to do something like this, be sure to check
your sub specs. My sub is meant for a small sealed
enclosure.

Bantan:
The enclosure is made of fiberglass and MDF. It is coated
with a rubberized undercoating for dampening purposes.
Attention to detail has resulted in very little to no vibration.
The enclosure fits very very very tightly in position.
If I had the time I would make one for you, however this
project was a real pain in the a__. There's no reasonable
amount of money I would accept. Stereo shops should be
able to fabricate whatever you want within a couple of days.
I was not willing to spend the $900-$1,000 the shops were
asking to do the job, so I just read about fabrication and
started building.
The speaker is a dual voice coil subwoofer rated at 500
watts.

WormGod:
I could not cover the speaker if I wanted to. Number one, I
picked the speaker because of it aesthetics (I want it to be
seen). Number two, it sticks out of the door due to the very
large magnet and because of volume requirements of the
subwoofer. I would have to disagree with you. I love the
way it looks.

Tone:
I lined the spare tire with masking tape covered with WD40,
but otherwise a similar idea.