Porsche 944s and 928s are far more rust resistant than most American or Japanese cars of the 80s or even 90s. Likewise with Volvos. The classic 911 was an old design that went through iterative improvements, and the 964 is better rust-proofed than most American or Japanese cars of the late 80s or 90s. Old Audis tend to have minimal rust, and old Mercedes-Benzes like the W126, W124, and W201, while they certainly can and do rust, their bodies tend to far outlast Japanese and American cars of the same era driven in similar conditions. Old W124s still soldier on as daily drivers and winter beaters in the cold and salty environments of post-Soviet states with mostly OK bodies, whereas Japanese cars of the 1980s almost all rotted away beyond repair being worthwhile more than a decade ago.

I came here to mention E-coat, though I'm thinking of it by another name, it's why in dry climates it's rare to see vintage fords rusted out, GM and Chrysler took longer to implement it.