I bought a 99' police interceptor crown vic and it was from harrisburg. It was the street appearance model not used in pursuits with absolutly a rust free undercarriage. I ended up using rust bullet on it and just spraypainted the frame every year. Of course now the frame has some surface rust, as well as the exhaust, but every year I just do it again. POR 15 or Rustbullet will certainly make it last far longer, but NOTHING will stop rust 100%.
Another way which is not popular, is oil and a dirt road. Nothing works better, cheaper. I would use the blackest, dirtiest diesel oil you can find and spray it on. Then drive on a dirt road. Instant red neck undercoating!!!:-laf All joking aside, my dad had new oil sprayed on his van, and it is not messy like you would think as did help slow the rusting over this winter.
Another way which is not popular, is oil and a dirt road. Nothing works better, cheaper. I would use the blackest, dirtiest diesel oil you can find and spray it on. Then drive on a dirt road. Instant red neck undercoating!!!:-laf All joking aside, my dad had new oil sprayed on his van, and it is not messy like you would think as did help slow the rusting over this winter.