Thanks again everyone for your feedback. It's great to see such a variety of experiences and advice. It's all over the place in fact
but I'm learning a lot.
Renting an RV is really not an option I'm afraid. We plan to take as much time as we need to see and do everything we want, and we may be on the road for anything from two to six months. A two-month rental might cost roughly as much as buying-and-selling but I think a six-month rental from a place like CruiseAmerica would send us to the poorhouse. It did occur to me that there might be a market for long-term RV rentals, either from a company or through some kind of marketplace website. Does such a thing exist or did I just invent the new Airbnb?
On balance, I think buying an ex-rental might not be for us. It's not the high miles or bare bones, though. I think that under the right circumstances it's an attractive proposition. With many Class C RV's the coach will wear out long before the chassis does and my wife has decreed that we actually want something simple. Honestly, if I'd had it my way we would be touring the country in a retro-fantastic 1970s GMC double rear-axle spacemobile but she made me promise that this trip would be about the journey and not the vehicle.
With that in mind I'm concentrating on practicality. I'm focusing on things like ease of resale and so the ex-rental is out. I'm now looking at RV's from around 2010 to 2015 with about 6,000 miles per year, give or take, and ideally in the hands of private sellers. There are several I like and I've made a few phone calls already...