I notice that my left rear wheel well has an area with a 2" diamater with the black coating material gone and so the metal in that area is being exposed. I certainly do not want to leave it like that. What kind of coating should I buy to do the patch?

 

Undercoating. Autoparts store. Comes in a tall spray can. 3M makes a good one.

 

If you go to auto body shops they typically have a product. The shop around me has a can they get from their vendor, I purchased two cans back in 2010, so unfortunately I do not have the brand and type. Auto parts stores have similar products, but with owning 40 cars, and living in Michigan, the auto body shops have a strong hold when it comes to better quality products vs. retail.