My 2014 coach had the exact same corrosion on the frame. Fleetwood stripped it and repainted it at Decatur. They told me the frame is supplied by Freightliner and prepped and painted by them. No problem getting it repainted even though it meant a lot of hrs to do it. I did document the rust and notified Fleetwood early in the warranty coverage.
Edit: I think I would contact Decatur and since you showed them the problem while still in warranty they might fix it for you since they gave you misinformation. Also Decatur is a Freightliner service center for warranty they should have covered it anyway.
Let us know how this turns out.
pointrow
