Diesel would be my choice. I have a 18' open goose neck trailer that I haul my Dart on. For several years I pulled it with a 2000 Powerstroke, now I pull it with a 2014 1500. I can tell you there is a difference, the worst mileage the diesel ever got towing was 13.6. If I were to ever buy an enclosed trailer I'd buy another diesel, probably a 3/4 ton.