around here, they use a salt brine on the roads - super rust producer !
my 99 caravan came from arazona, and had zero rust, so for the last 9 years since i bought it, my buddy has oiled the pi$$ out of it every fall.
i drilled several 3/4" holes in the doors and the hatch, plus several above the foam in the dog legs.
i take out the tail lights and all the rubber body plugs, as well as pull up the plastic carpet sill plates so he can slather those areas as well.
by removing the tail lights, he can blast the quarters and get a bunch into the area where the wheel house and quarter lips come together.
he also gets the front fender area at the bottom where the foam used to be, then does the underside.
that thing marks it's territory like an old harley all the time !
but to this day, it still isn't rusty !