Aftermarket Stereos

My plan is to wire a 3 channel amp in the trunk that will power 2 6x9s and 1 sub. I will put the sub in a free standing box in the trunk. The 6x9s I am thinking I will mount to the underside of the rear sill (depending on the mounting pattern I may fab an adapter).

I am then going to run a line to under the drivers seat that I can plug an MP3 player into. This way I can run all my car audio off of an mp3 player and I don't need to worry about mounting a head unit.