I've only ever toured on an aluminium bike, and as such have never had to worry about it getting wet. As I've only toured in fairly wet environments (the UK and Patagonia), this has been a good thing.
Is it different touring with a steel bike? If you were touring for several months through a wet environment and camping in tents most of the time, would rust be a serious problem that you'd have to face? And if so, what do you do about it?