I know that my in laws 2001 jetta, when we removed the panels to replace broken power windows brackets, the inside of the door cavity was covered with a waxy coating. Also, from what I see on the road, other German cars seem to be holding up much better than the rest when it comes to rust. It is also easy to spot if these vehicles had any body panels replaced, because they are the only ones with rust.
On the other hand, my 92 Corsica, 91 Tracer, 95 Accord, 2003 Focus, 2006 Mazda 3, and 2015 Grand Caravan were all bone dry inside all the cavities that I've seen.