It takes roughly 25sq foot of Edead to do 2 doors with one layer. The better one is Edead v1 SE, and depending on how much dampening you would like depermins how many layers you should laydown on the door.
I'm not to sure what outside vibrations are, i will asume that those are things like your side mirrows, or loose door handles. Assuming that this is the problem i would recomend you lay some mat between the speaker and the door, so that it absorbs the vibrations. While your at it, i would recomend that you mat the whole door, so that you can reduce the amount of sounds that come through the door, making the ride quieter, and the music sound louder.
Hope this helps.