What size Class C are you looking for and how much do you expect load in the RV. I have looked at many Class C's and found many longer Class C's to be near maxing out on weight before the owner added added the groceries. The Super C's have a heavier frame, So that said, what is your planned use. Are you going to be 3-4 hours a day, driving maybe 15,000 miles yearly. The diesel may more sense. Driving shorter distances go with the gas. Presently, I have noticed the price of gas and diesel (with fuel card) and nearly the same, not the dollar difference not long ago
A school system had several small trucks and they specially would look and spec only gas trucks that starter easily can be changed and door hinges easily replaced. Look over you what need, Modern trucks are quieter by either noise reduction in the engine or better insulation in the cab. Does the Class C have front end insulation.
Clay