Actually, fishslayer, with my Open Roads and Greenlane diesel fuel cards, probably more than half the time during our travels, we paid less for diesel than what the posted price was for 87 unleaded. As an added benefit, we used truck stops such as Love's and Pilot/Flying J's, where there was plenty of room to maneuver and pay at the pump. I would also expect a Ford V8 Class C to average 9 mpg at best, probably more like 7-8 mpg, whereas my diesel averaged between 10.5-11 mpg.
Yeah, if it wasn't the cost of repair and upkeep, I'd stay with diesel, but those $$$$ far outweigh a couple of miles per gallon less in economy.