The wing/fender area is considered as a cosmetic panel that does not contribute to the energy absorption during an accident. Wings and fenders do not therefore form part of any imposed structural survey for roadworthiness.
It is common to find rust at that bottom and rear bottom sections of fenders. These areas collect significant amounts of dirt and road debris to initiate a special crevice form form of corrosion called 'poultice corrosion'. Most often, it is the lower rear portions of the front and rear fender wells that suffer the most frequent and severe rust damage. The main reasons for this particular behavior are twofold (reference):