In the past I used Rust Check with poorish results. Switched over to Krown on my last two trucks, huge rust on my '03 due to what I feel was improper application. Found someone that applied much better when I got the '11 but did have several issues related to the product itself. First, all door rubbers on both my truck and Kath's car are 110% screwed. Previous store operator said no problem they'd look after it but he's gone and Krown told me to buzz off. Second, on the truck, caused an issue where the plastic fuel pump module would become conductive across the top causing intermittent poor running and the gas gauge going berserk. Replaced the module plus sender after being assured by Krown it was a total fluke only to have it happen a second time. Third, truck saw little to no gravel roads but did have paint peeling on the fender lips and some rust starting. While it's a filthy mess much of the summer I'm anal about washing in the winter. Hard to say if it's a GM paint issue or Krown but rust is for sure on their heads.
Fast forward to my new ride, considering Corrosion Free, does anyone have long term experience with it?