After reading this whole topic, I had a minor heart attack and ran out to my truck to see if I had rust underneath my truck. My last truck (2004 Silverado) had frame rust everywhere. Thank goodness, mine shows very little signs of rust. It is a southern truck and was built in Indiana (not sure if that changes anything).
Wanted to share this picture to show that this happens in places that don't get much salt too. This is a truck for sale in OKC that is decently priced, is the All-Terrain package, and would look great cleaned up. I'm sure the dealer doesn't even realize his picture is showing an issue with the truck, but if I saw the price tag on it and saw the rust there, I would walk.