Carmakers avoid designed-in moisture pockets, vulnerable panels are galvanized both sides, bodies are fully immersed in rustproofing chemicals and many components are non-corroding plastic, all backed by a lengthy warranty. Do you really think a marijuana-buzzed high school dropout drilling holes in your new car, perforating the factory sealants and spraying smelly glop will add anything? I don't think so, and it may damage the car and void the factory warranty!
Some products are $750 one-time waxy coatings. Dirt, debris and dust collects in chassis nooks and crannies, door pillars and inside doors, the areas targeted. Wax-coating dirt does nothing to protect the underlying metal. Warranty compensation is difficult to collect.
An alternate is the annual $125 oil sprays. They are ineffective for similar reasons. Warranty compensation is difficult to collect.
Rubber or asphalt based $500 sound suppressant undercoating actually promotes corrosion.
Disreputable car dealers and auto supply stores sell electronic rust protection modules. Prices range from $150 to $2,000. The LED indicator lamp is the only thing that really works! The National Association of Corrosion Engineers (NACE) says they are ineffective for vehicles. Cathodic electrochemical corrosion prevention is valid only for boats, bridges and pipelines where electrical continuity can be maintained through seawater or soil. Warranty compensation is difficult to collect.
Instead of pricey rustproofing sprays and gadgets spring for quality mud flaps to protect the car from stone damage, fix paint chips and scratches quickly, and wash the car frequently in the wintertime.