I think they've paid more attention to corrosion protection than in the past, but I don't think a rust-proof car has yet hit the streets. Take a look at my Underbody Pics thread and you can see there are not nearly as many uncoated stamped steel components underneath as you'd find in an older (or lesser) vehicle.
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CT6-V underbody pics
I'm assuming a lot of commonality with the other CT6 trim levels. These pics are for anyone who hasn't had a chance to jump under the car when it's in the air. Starting from the rear and walking forward... 1) Rear view of the exhaust, rear steering actuator, differential and fuel tank. Note...