it is just the same here , it is not uncommon to see that , my trucks rockers are gone & I have already replaced the box & I live in a very dry climate , if you have salt like that & live in a moist climate you can be in a situation where the car needs to be replaced in 5-6 years even with the oil / anti rust spray treatments
a friend has 2 Iroc R/Ts he has meticulously maintained 1 was kept in Ontario for a few years , it has lower milage but the corrosion on the alum & the whole car is far worse then the one kept in the west , the reality is there is not a lot you can do to prevent deterioration if you live in a moist climate which is why I would never again live near the great lakes