Rust protection...

When I bought the Bullitt, I decided against any sort of rust protection, undercoating, etc. with the thought that I'd keep the car out of the winter salt. Consumer Reports also once mentioned to avoid all of those add-ons because they usually aren't worth it. This winter, the car is stored away. But I'm not sure I'm going to have a "winter beater" next year...

One thing the dealership told me was that they need to put on any rustproofing within a month or so of purchase. Is this really true or were they just trying to get extra business? If it's not true, I'd consider having the car rustproofed this coming summer (Simonize?)... Any advice?