I can't believe VW is still using those foam blocks.
Here in Vancouver area don't really see a lot of cars with corrosion issues, however, a lot of older VWs have that classic rust in the fender from the foam blocks. When my mom had her Jetta I took those out before any rust started after seeing lots of Jettas and Golfs here with rusty fenders. I would also spray the fender corners and arches with Rust Check before winter, and when she sold the car after 21 years it was completely rust free.