This may be a bit off your original question, but if you can go to mid 90's look for a low mile Toyota with a V-6.
Just as a truth, often you'll find many gassers get bad due to age, lack of care, but also mileage is tough. You can find a boatload of them with 30k miles for sale, with over a decade on them.
With Toyotas you often do not find that. I've seen people with over 300k on their Toyota based class C (v-6), often getting 17mpg which will save gas money. Mine is a 4 cylinder, underpowered, but I still go 60-65 like everybody else.
Just wanted to throw you a curve ball in your consideration. In my opinion, a great RV would be a good used Toyota based class C, mid 90's ish, bought from an elderly couple with less than 50k miles. Clean & garge kept etc.
4 whopping cylinders on Toyota RV's. Talk about great getting good MPG. Also I have a very light foot on the pedal. I followed some MPG advice on Livingpress.com and I now get 22 MPG! Not bad for a home on wheels.