I would be seeking some legal advice at this point because I would be less than happy with anything other than a complete rebuild on a new chassis and I suspect this is not a viable option with a motorhome. You may need to formally notify the dealership that supplied the motorhome because it is them you had a purchase contract with and it is them who will be liable for buying the vehicle back if Ford do not replace the chassis to your satisfaction. They and the manufacturer of the motorhome will carry more clout with Ford.