A few more answers: My 2013 and 2015 Dometics failed from Freon loss as told to me by the service man, likely caused by a leaking evaporator with lubricating oil all over it. Strikes me that that voltage problems would be more likely to cause compressor burn out than Freon loss. I am very voltage conscious. We haven't had my son't Coleman diagnosed yet--he is currently baking in a hot campground for the weekend. His previous AC lasted 9 years before the unit was sold.
From the responses and my own family's experience, I must conclude that around 2012 when significant Chinese manufacturing entered the business, the longevity plummeted. Those with great stories were built before then, including both myself and my son.
While ordinarily shy of extended warranties, it would seem to be a no-brainer in the case of an RV AC.