When I was having my new hood built by some custome fabricators, they took the Crossfire hood to have it acid dipped to remove all the paint and primer. It had to be dipped 3 times to get all the primer off. So Karmann must coat them fairly well with some pretty good stuff. (Just not the doors)
What looks to be another weak point on our cars when ever rust is brought up seems to be in the area of fasteners, bolts, screws, etc.
Under the hood you may find several places where a rusted bolt transfers its corrosion to the surrounding "painted" metal. It's very easy to spot on a white car.