In my experience, using rubberized undercoating is just a bad idea if you are in a rust prone area. I applied the stuff to parts of my frame to protect' it from rust. ... In fact, the added cohesion can exasperate the problem, allowing rust to spread at alarmingly fast rates when it is designed to do the exact opposite.

Why you should never undercoat your car?

It can get into your metal wires and cables, affecting any component which is comprised of steel or aluminum. Even your transmission and engine have exposure to rust when there isn't a vehicle undercoating applied.

Do you really need undercoating?

Unless you are in an area where a lot of salt is used to clear the roads of ice and snow, undercoating is probably not necessary and can add significantly to the cost of your new car.