On Mon, 28 Mar 2016 18:12:05 +0200, Tom Ivar Helbekkmo
wrote:

Ed Huntress writes:

You're talking about old cars and trucks, which is what you have. New
ones are vastly better in terms of rust-resistance.

Seems they're getting less so, though. A neighbor of mine works at a
garage that preps new GM cars for sale. The cars have come across the
Atlantic by ship, and the first thing they have to do to them is remove
the rust that has accumulated in the weak spots, especially along the
welded seam at the bottom of the doors. Didn't used to be that way, he
says -- and he suspects it's simply about the quality of the steel.

-tih
It's the quality of the assembly, sealing, and finish

GM door seams and edges rust - particularly on their lower end
vehicles. This is not new, and they don't have to cross the Atlantic
for them to rust. A good soaking with an oil product - the lanolin
products are better than most but any oil will help - gives them a
fighting chance.