Agree - factory service in Decatur, IN, is your best bet, but for a major job like that, it isn't going to be cheap. If you just have some rust scale on visible parts, you can get it brushed clean, treated with something like POR, and painted for a lot less, but if the understorage is badly corroded and needs replacement, I would want a factory job or an RV repair specialist.
What part of the country are you in? Maybe someone can recommend a shop in your region.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL