I live in snow/salt country (upstate ny).
1. Pick up a few cans of 3M rust proofing spray, only available currently at body shop supply stores. It is a yellowish wax that really prevents rust in areas that are currently rust free but likely to rust. Bottom of doors, lips of the trunk, wheel well steel lips, etc.
2. Pick up a few cans of rust neturalizer gel. Apply this to your rust and it will turn black. They cover with paint or 3M rust proofing spray. Good for bolts and suspension pieces such as strut towers that you would not want to pay to fix or replace.
Both are proven methods that are relatively cheap, easy to apply and you can do it yourself. Commerical rust proofing is a total ripoff, IMO.
Richard.