Rear hatch rust

[terrence]

I'm sure everyone here has had to deal with the issue of rust under the weather seal on the rear hatch. Since the rear door on my brown van was in better condition I swapped them before it had to be sent off to the scrap yard. I repaired the rust and sprayed it to match but I was wonder if anyone knows exactly the cause of the rust build up in that area and what has been done to prevent it. I am thinking of putting a little bead of urethane left over from my windshield install around the problem area to see if that remedies it.

https://i.imgur.com/odttMlN.jpg

https://i.imgur.com/2sKvSgF.jpg