Extended warranties are really insurance policies. Never purchase insurance to cover anything you could not cover yourself. As an example, do you have insurance on coffee maker? Of course not- if it broke, you could just go buy another. Do you have insurance on your new dually pick up truck? Of course you do- if it were stolen or destroyed you probably could not easily just go buy another one! Could you easily pay to replace a circuit board on the RV's water heater? If yes, then the extended warranty is not for you.
Two more issues: one read the actual policy (contract) not the sales brochure. You will be surprised what really is covered, how any payments are made, and the confusing language as compared to the brochure. The other thing, when you buy that extended warranty you are covering yourself twice as you have a manufacturer's warranty at the same time you have that extended warranty.