An "extended warranty" is really an insurance policy. You pay a premium and they promise to fix certain things if they fail. Remember, the odds are not in your favor. If they pay out more than they take in they loose. Most of these "extended warranty" companies have access to repair records so they know what typically fails, and excluded those parts from coverage. Some companies make you jump through extensive and complicated hoops to get payment. A classic is their inspector must look at the failed part before approving. The inspector takes weeks and weeks before the inspection. Mean while you are without your RV and the repair shop wants it out of their way.
Before buying an "extended warranty" read the actual policy not the ales brochure. Understand exactly what you are buying.