Bob: It's not specifically an undercoating - more of a metal protectant like Schaeffer's 163. It's a wax&solvent mixture in an aerosol can. Sprays on and dries within seconds leaving a wax coating.
Pretty good stuff. I've used as a protectant on the undersides of my cars and around the house. Works well as a lubricant for old fashioned door hinges, the type with the removable pin. I remove the pin and knock off the rust with steel wool then give it a short spray with the MPHD and put it back together.