Rust is common of Motorhome and trailer chassis's. It is surface rust and it has been there for the 35 years I have been a RV tech. Occasionally we get a customer that goes crazy over this surface rust. If it bothers you, just spray paint with Rustoleum. In 35 years, I have never see a chassis break or fall apart from any "rust". When the Motorhomes chassis are sent to the manufacturer, they are NOT covered in shipment and they are stored in a field/parking lot before they are staged inside the OEM assbly plant. There is also the issue of the NEW motorhome transported to dealers in the rust belt of the USA during winter conditions. Most OEM's send out bulletins in the fall to remind those dealers to wash out the undercarriages after taking delivery from the OEM during the winter months. MOST do not. Doug