A car doesn't have to be driven in winter to rust.
From what I've read that front jack pad area is notorious even in countries where the roads aren't salted in winter.
Second to driving on salted road for rotting out a floor and rockers is parking a car on grass. Put it in your side yard, mow around it and check it 3 years later. Everywhere that grass touched will be very rusted, and the underside will be quite rusted from being damp for the whole time.