I live in a country with very harssh winters. Norway.
In addition, they use a lot of salt to keep the roads free of ice, so the snow that falls turns into a salty slush. VERY bad for cars, and creates a lot of corrosion problems.
Becuase of this I had my 3IS (is 300h, hybrid) coated with a product from dinitrol. The proper term if tectyl (google it)
This is a form of that black sticky stuff mentioned earlier.
I have not had any problems, other that the smell of burnt tectyl from when the hybrid system works hard and the electrical components become warm.
But you have to take your car to someone professional. Someone that know what they are doing, and covers up all hot and moving parts before spraying on this stuff. You do not want this stuff on your engine, transmission, brakes, driveshaft, damshaft, or dampers. Some places it is can limit heatflow away from hot components, some places it can mess up electrical stuff, and some places it an cause unbalance in moving parts.
So if you can get it done somewhere proffesional, i would absolutly recomend it. It does protect the car a lot from rust. And if done correctly, it will not interfere with your cars systems.
however, if done incorrectly it can mess up electrical and mechanical stuff.
as mentioned I have done this to my car, and it is not that hard. But make sure the people doing it know what they are doing. Otherwise it will mess up your car.