I don't believe in washing it off every week. I don't like the idea of water finding it's way into those nooks & crannies, freezing and expanding in the process causing whatever kind of damage that stuff does. I haven't washed my '89 K1500 since I bought it.. Wheel lips were already slightly krispy, rockers were already gone. I have Krown T40 applied every year and then touch it up myself. Floor pans, frame & metal lines are still clean as well as the axles and such. I expect any edge to crust up with cancer so I wasn't worried about that when I got this truck.
But as one member pointed out that even with no salt things can still crisp up, that's because of the coating system's life span as I mentioned earlier. What puts a drain on it is moisture/humidity and when you combine salt with that, it accelerates it. So even vehicles kept in arid climates still don't have 100% of their coating life, which is why you'll see rust in just 2 or 3 years once they're exposed to a musty, humid garage or even worse, salt. The hot & cold cycles 4 season areas see don't do wonders for corrosion either.