I am getting ready for a 325, so i am trying to get as much money as possible
i dont really want to sell this, but i might depending on what it is worth to others...
this is a custom made sub box for e36s, not sure about other body styles, but e36 is a perfect fix. It was fabricated by El Presidente (one of the main sound guys that was on bmwforums and i think bimmerforums).
It has a build in amp, it is a Blapunkt (spelling) amp in it, dont know too much about amps, but it seems to work really well with the infinity ref 1230 12 inch sub.
This fits in the back of your trunk, taking up hardly any space.
it adds the low end that is missing to you bmw sound system.
right now i have an alpine HU and inifnity ref speakers all around, and with this sub in my trunk, it does wonders.
here are a few pics, more if wanted..