The doors on the steel trucks, when being assembled had wax daubs applied to the inside of the outer skin. There were three small holes in the bottom of the inner panel. When it went into the corrosion dip tanks, the three holes allowed the chemicals to drain. After it was painted and the vehicle went through the paint ovens, the wax melted and the holes were plugged. The door was sealed and remained dry.
The new doors, for whatever reason, are being used to funnel water. The holes in the bottom of the door are remaining open to channel water. That is, IMO, where the corrosion and water problems are stemming from. It's almost like because Ford made the truck aluminum, they don't care about water seepage anymore.