2013 Silverado undercoating

[Tomo]

Not sure if this has been discussed here before. I bought a new crew cab z71 back in 2013 has about 35,000 miles now. Very happy with the truck except for 1 thing last year I noticed that the factory coating on the frame was coming off in large areas. I took the truck to the dealership and they told me that GM has issued a bulletin for this issue. They stripped the frame while on the truck and painted everything they could get to - following the bulletin instructions GM put out. Has anyone else had this issue? I bought this truck with the intentions of having it for a long time and I am still concerned about the top of the frame, the inside of the frame & the other parts they couldn't get to - these areas are showing small rust spots.