I own a near mint condition (minus a few scratches) Colorado bought straight from the dealership only a few days from its factory. Ever since then, it has gone through some tough winters, but we have always washed the under body and made sure that salt and snow were not present, However, despite this, everything that is metal underneath has a thin layer of rust on it. This is apparent with the muffler, which has a hole in it that you can see shoots water out of it when you start the car from letting it sit overnight. One inspection, and I knew that the muffler would have to be replaced, as the entire back and some of the bottom was composed of rust. This water problem happens at all times of the year, but it is most apparent when the air is humid for obvious reasons.