pretty good writeup, but I must add that to this on the door panels, ( maybe I just didn't read it or I skipped over it ) on the door panels, to better reduce outside noise and to even further reduce speaker resonance, It is also highly recommended to put whatever brand of insulating ( dynamat stuff or whatever you call it ) on behind the door panel inside the door. that will reduce resonance from the exterior of the car also and it will definantly help the inside. I did that with my car, and the difference is like night and day. a very easy way to tell is to open and close the door, if you hear things rattling and the overall feel of the door closing sounds like a metallic thud, doing this will greatly reduce that.
I will also second the MDF being used as a speaker baffle, I did the exact same thing with my car. I think we use more MDF in our shop than anything else.