I'm thinking about a new concept for a hifi install in my Y. That is why I'm selling my current hifi install (without subwoofer itself and amplifiers). This install is made of "glass fibre reinforced plastic" and medium density fibreboard.
It's very stable. The housing for the subwoofer is optimized for a 12" subwoofer, is 100% sealed and has a volume of circa 30 litres. A speaker terminal is also fitted in the housing at the front side. Between the back side of the trunk and the front side of the subwoofer housing is some free space to place one or two capacitors or some stuff like gloves. 
Although the sub-box is closed the sub (my Hertz ES300) plays very well deep dropping lows. My sub in this housing drives fantastic.Here are some pictures of the building of this box:
The boards which are shown on the last image are not part of the selling. They have a lot of holes and fitments for different amps and capacitors. If the buyer likes to have these boards I will ship them too (without additional payment).
All in all I think about 115€ for the whole install (without sub, amp, caps, etc.). I actually don't know about the prices for the shipment. It depends on the country.
If you have any questions please don't hesitate to get in contact with me via this board are send me an e-mail to: jendevi@hotmail.com
Bye!