How can I removed years of rust from an outdoor dog kennel?

There's a product called Rust Converter by Klean Strip. I think you can get it at Wal-Mart or Lowe's. You get as much rust off as you can by brushing with a wire brush or sanding it off, clean the surface and let it dry, and then apply this stuff. It converts the rust to a black primer that can then be painted used 24 hours later. It says that it can stain other materials and to wash immediately with soap and water. If it's important to you, I'd tape up the plastic so that the rust converter wouldn't get on it and remove the tape when you're done.