In my personal experience and readings over the past 40+ years, diesel engines have generally delivered slightly better MPG vs. a gasoline engine. However, nobody buys a turbo diesel engine powered truck or RV just for the MPG advantgage. Trucks & RV's with turbo diesel engines are purchased for the huge performance and longevity improvement over gasoline engines. People who operate turbo diesel engines usually don't get rid of their turbo diesel powered trucks & RV's because their engines blow up. They get rid of them because they finally get tired or bored with them after 10+ years or 700K miles of use and simply want something newer! You can buy a diesel for long term heavy duty use ONCE, or a gasser more than once. Gasoline enginies in trucks and RV's have their place. Let your pocket book and need for longevity be your guide.
JMHO.
Happy camping!!! See y'all down the road!!!:)