I took the opportunity to walk through my old PD's fleet services department many times over the years. It was amazing looking up at the various cars while being serviced. Gray, mostly gray, a bit o' brown, some lube stains here and there, but NO rust. Exhaust systems never rusted as they were always hot. Run a car 24/7/365, give it a bath on a regular basis, and you will mostly never see rust. Yes I am well aware heat rusts metal, rust is really just fire slowed down 1000's of times, yet hardly ever was an exhaust system replaced on a car. I have seen exhaust manifolds warp, paint get a bit dull, and well extreme wear on the interior, but rust wasn't an issue. Pop the hood and you'll see the same as the undercarriage. "There's a motor in there?"
Sitting still is quite another matter for a midwestern auto.....................
Now here in the desert, faded paint, cracked rubber/plastic/vinyl, but NO RUST.
G