The holes are drilled to allow access for the sprayers to spray inside the doors, etc. They don’t put holes in to drain the cavities.
Really though I used some wax type coating from NAPA when I re did my door. You could do it yourself by taking the door and back panels off. Also I used a product called Rocker Schultz on lower exterior surfaces to guard against sand blasting. Spray it on and paint over it. Very tough stuff.