I suspect that sound deadening the floor and trunk is more effective than the doors, simply because it's a larger area. What I did with the doors is remove the foam moisture shield, and after removing the wiring, apply strips of sound deadening to the exposed metal. One sheet was enough to do all four doors (not much metal on rear doors).
FWIW, on BMWs dynamat is only applied to the floorpan of the chassis, rear bench, and trunk. Their door panels are a quarter inch thick though, instead of thin plastic like we have; I assume that provides adequate insulation.
