I bought my pre-owned 2005 Ford Escape in 2006 with 20,000km. The day I bought it, I had the dealership ad an aftermarket trailer hitch and a Rust Control Module.
My research of these Modules led me to believe that there was something to them, due in part the fact that the Canadian Coast Guard and Navy have them on their vessels.
While it is true that the vehicle needs to be grounded for the Module to actually work, (for our vehicles that means the tires have to be in water,) winter time is when we need protection the most, (salt & water) and when the tires are wet most of the time.
In conclusion, that cheap hitch I added-on five years ago should by now be rusted beyond recognition, but it looks like the day I had them install it.
My vehicle's overall condition is excellent, and you would have to be hard pressed to see any rust anywhere.
Now whether the Rust Module has anything to do with it or not I don't know... What I do know from experience, is that usually my cars show their age, particularly with our Canadian winters and Ontario salted roads.