Rustproofing, if done right, is a good thing and worth the investment.

The reason many people think they are bogus products is that they cannot reverse rust once its started, nor can any product or process (short of cutting and welding in new metal) properly "fix" rust. No magic coatings, no potions will do this.

Wurth makes a product I use frequently on newer cars, or on recent restorations that I highly recommend. Its called body wax and is a light product that is sprayed via a flexible wand into rocker panels, wheel arches, etc. The idea is to coat the metal with a greasy layer that prevents water from causing rust. Its light enough that it does not cause drains to clog.

The one caveat I need to give is that modern cars are much better at proper and effective application of seam sealers, undercoats and primers than the more elderly models, but no one's pants ever fell off wearing belts and suspenders!

For what its worth,