[focusracer]

Problem with using stock headunit is that there may not be preouts for an amp. Here's a link for building a fiberglass box, I found it somewhere on a focus forum, forget which one.fiberglass box
Also, I posted some pics of my box I made over on focusbc, here's the link for that,sub box I removed my spare tire and built it in there, I have full function of my trunk/hatch but, no spare tire. Fiberglass is the best way to do a box and is a lot easier to do than most people realize. I used tin foil to line my trunk before laying in the fg, the installer where I buy all my stuff told me it works better than plastic and doesn't stick like plastic either.