Once you've narrowed down your choices, I think you'd be well served calling your favorite local RV service center, plus some random RV service centers (ideally on routes to/from/at areas you visit), to find out if they accept that particular company/plan. Just as important is any input they may have about the quality of service/coverage provided. Their feedback would carry a lot more weight with me than any anecdotal online inputs.
Also, pick a well-known, reputable company that's been in business a number of years. Many new extended warranty companies promise the sun and the moon, collect money from several hundred/thousand customers, then declare bankruptcy.
FYI, very few (if any) extended warranty plans cover the frame, structural issues, and/or water leaks (neither the leak itself or the resulting damage). These are the most catastrophic in terms of repair costs, which is why they're rarely, if ever, covered.