Warranties are profitable for the companies that sell them. Note that Clark Howard, a consumer advocate, says to stay away from them, http://clarkhoward.com/shownotes/2005/12/20/
An RV consists of a chassis and the coach. The chassis is a tried and true commercial vehicle. The coach is a structure that holds furnishings, appliances, and electrical and water systems. If you follow the operating procedures, do the scheduled maintenance, and actaully use the RV routinely, you should get years of service with few problems. Disuse, misuse, and lack of maintenence are the enemies of reliability and availability.
Put the warranty money in a savings account. If you don't use it, it's all yours at the end of the warranty period.