2016 regular cab, purchased new 3 months ago (10/1/2016). So I stumbled on to this thread last night and read it start to finish. I live in extreme South Texas - it snows here about once every 100 years. Rust no problem, right? Wrong - extreme high temps and humidity and lots of salt air. No problem - keep the truck in the garage overnight and a good carnauba wax job. Never thought to worry about the frame. So I crawled under last night, after reading all these threads, and yep, some bare spots, with metal exposed. Probably the result of rocks/pebbles on caliche roads. I was surprised at just how thin the wax coating is. No, I'm not taking it to Chevrolet - as someone suggested the only way to do this is sand, prime, and some black enamel paint in the affected areas. But this changes everything - no underneath power hose sprays like a used to to with my Jeep after beach running. I'd crawl under the thing and scrub/wash the frame. That will pull the wax off. This changes everything - I'm 71 and continually sanding/painting the frame is going to get old very fast.
I'm not new to Chevrolet - been driving their pickups and old style Blazers since the 1960's. Had to deal with the surface rust on the body, but never frame rust until a 2004 which I had purchased used, sight-unseen, from PA. My sister, who lives up there, had checked it out, said the body was perfect. I guess she never crawled underneath it. When it got down here - large chunks of frame rust started to peel off. Spent a lot of time scarping the thing, then undercoating it. I attributed that to the PA climate. Never dreamed that the frame wax was over bare metal, so never thought that was an issue when I bought my 2016. It doesn't take a Ph. D. in automotive design to realize that wax over a bare metal steel frame isn't the greatest for long term longevity. When did GM start this process - I'm thinking with the 1999 or 2000 models.
Most owners don't crawl under their vehicles and check things out like we fanatics on these forum do. I was really happy with my new 2016 (no vibrations or any other problems) until this. It's going to be continual long term maintenance - much more involved than the twice a year clay bar and waxing I do to the body.