I also declined the extended warranty on our 2011 Sunseeker 3100, which is on a Ford chassis. It appears that the chassis seldom gives problems (how many used RV ads state trans or engine has been rebuilt?) and has a long warranty. The appliances had a 2 year warranty so the extended warranty would only be covering the third year. The cost of it would have paid for a new refrigerator and then some.
If you can fix things yourself, or educate yourself to the point where you can, you would probably come out ahead without the extended warranty, even if something broke. Look on line at prices for a replacement air conditioner, furnace, water heater, and refrigerator. You can replace any of these yourself. A convertor may require electrical troubleshooting that some aren't comfortable doing. Same with the generator but I don't hear of many failing electrically.
The main questions are how much will you do yourself and how much risk are you comfortable with. Also consider how much will you have to pay for service anyway as deductibles each time you take it in.
In two years we've driven ours 21,000 miles and camped about 250 nights. I've only changed the oil and filter in the chassis. I had to modify the hood vent flap (it was junk) and adjust the water heater ignitor electrodes. Those are the only repair issues I've had. We've had some minor problems (cabinet door lift struts, 12 volt receptacle pulled out, etc.) but they were easily and cheaply repaired.