Potential problems with "any" plastic sheeting, and mattress bags, they not UV resistant and it falls apart over time. Same with duct tape, the adhesive dries out and it falls off. Let's do repairs that will last.
I can hear the comments already, no sun behind door panel, car always in garage. This stuff is made to fail, not to last. Original Chrysler water shields don't fall apart under normal use.
I took door panels off at salvage yards and plastic bits went airborn and all over the area and inside the car, just a big mess. You wouldn't want that in your classic Looking at it it was a brown garbage bag.
@Dean Prevolos look at the door and quarter, at the bottom of each there is a long straight line that 2" of the plastic gets tucked in to. So water doesn't run out the bottom and inside the car.
3M strip caulk works great for this.