What I used to do in my old VWs was plug the drain holes and fill the bottom 2" with a wax based preservative.(Waxoyl)
I would then leave it for a few days then remove the tape from the drain holes and clear the drains.
The excess would drain out,coating the inside of the door bottoms.
After another few days the remaining preservative would have set and you're good to go!
This method is best left 'til after any paintwork.
I'm planning to use this technique on my own doors.


1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.