Krown provides a rust proofing treatment that is applied annually. The reviews on it are very good, they have been in a business for a long time, if it is something you are interested in it is worth looking up. I use it on my daily driven Subaru BRZ because I would like the chassis and body to last a good long time rust free.
If you get the car treated early enough, i.e. within 6 months of purchase, Krown will guarantee the car to be rust free for life.