Mick,
I've posted before about this, I recommend and panel beaters use "Waxguard" around the joins in all panels. It excludes water AND dust and is used on many new cars.
RET is correct, paint the sound deadener on the inner door panel first THEN paint on the Waxguard. I painted the waxguard liberally inside the door so it ran out the drain holes, then after it had started to skin put paddle pop sticks in the holdes until the waxguard had set. Drain hole still works and waxguard fills the join between door skin and door frame. No rust, and NO DEAD FISH SMELL
Cheers,
Craig.