What's going to likely fail in 5 years, on a brand new 5th wheel, that'll cost you $1800+ to repair? Probably not a good option.
For me it was replacing shackles in Whitehorse Yukon, a burned out motor in the self leveling system, awning replacement motor. All expired within 6 months of the dealer warranty. For me it has paid for itself. That being said as a general rule I don't buy extended warranties, this being the exception. I knew when I purchaed the unit I would be putting on a lot of miles for a lot of years. Trailers are built from the inside out and the major cost of repairs is labor. If an appliance needs to be replaced sometimes windows have to be removed to get things inside and out. If you plan on limited mileage with a limited holding time, I wouldn't do it. But for me I've got over 20,000 towing miles and over six months occupied time when all the systems were in use and that is likely to double or triple over the next six years of my warranty life. Oh...one other thing. When it breaks it will likely be at the worse possible time.