I'm in the "wondering" phase on buying a Class-C and saw this thread. From what (little) I know about C's I was disappointed there were not more diesel options and been hoping I'd just missed them. When we got our first RV I really agonized over the gas/diesel question and ended up buying the diesel. Ironically that was when diesel fuel cost LESS than gas and since I bought that truck (to tow a FW) the costs flipped and never went back...
Still - having owned two diesel RV tow vehicles I am a big fan. I guess I could run the numbers and convince myself that operating cost (eg fuel economy) is largely offset by total cost (factoring in acquisition and maintenance). But one thing I really loved about both my trucks was the effective cruising range. My Dodge could go almost 400 miles and the Volvo was as ridiculous 1800.
I do know it's all in the numbers but somehow having owned a rig that grossed at 15 ton and got 9 mpg it annoys me to contemplate something that will weigh so much less and not even manage 8...