I am not convinced of the value of extra rustproofing anymore.
Both of our current cars are at almost 250,000 km's and over 8 years old, we do nothing special in terms of care.
The Civic has surface rust on nuts, bolts & brackets only, nothing on the body.
The Volvo is devoid of rust completely.
I believe car manufacturers have made great strides in terms of the metals and protection provided from just the factory treatments, but I can't discount the value of extra protection. Krown and Fluid Film tend to be the prefered chemicals by other posters.