I just noticed the paint bubbling up from rust on my 2 1/2 year old Sprinter. It was a small spot near the water inlet. I pulled the fitting off and found considerable rust. I pulled off the electric inlet and it was even worse. Lots of paint had gone away. Turns out every hole Sportsmobile cut was rusting away. I sanded the rust down to bare metal, primed and painted. I'm so glad I found it when I did. I don't know why Sportsmobile didn't prime the cuts.