What protects parts such as the door of a car from rusting?
You can use rust prevention and protection products and sprays
at Noxudolusa.com. All these products are engineered to stop and
prevent rusting
What can I buy for my car to protect the underbody from rusting?
There is a product called fluid film that protects underbody
parts from rusting and also has superior lubrication for moving
parts. Here is a link to the product http://www.fluid-film.com/ I
hope that helps you.