The standard way the PPF is applied would stop (cut) the film just above the plastic fender flairs and above the door trim plastic. There is a gap between these plastic pieces that allows water (and the water/salt brine from winter) to run behind the trim. It will sit on the paint and on the lower edges of the fenders and door bottoms. These dark and damp spots that you can't wash/see and dry are typically where rust will start. So the film i had applied covers the metal behind the plastic and wraps under the vent flange of the wheel arches and around the back side of the door weld seams. This in my opinion should greatly help with rust. If you are not in a rust belt (or NE region) this is of less a concern as the dirty water that collects behind the plastic has less salt in it.