This is a paragraph from the current Michelin RV Guide:
While most tires will need replacement before they achieve 10 years, it is recommended that any tires in service 10 years or more from the date of manufacture, including spare tires, be replaced with new tires as a simple precaution even if such tires appear serviceable and even if they have not reached the legal wear limit.
For tires that were on an original equipment vehicle (i.e. acquired by the consumer on a new vehicle), follow the vehicle manufacturer’s tire replacement recommendations when specified (but not to exceed 10 years).