Tony,
I wondered about that, if the mileage is that close it would not be worth it. And I quite frankly love the sound and performance of the 8V92. Your coach is probably a 45' which may make some difference. I assume you flat tow your Jeep Liberty which should be next to nothing in weight and wind. Our Liberty weighs 43000 lbs. and with the smaller trailer and our diesel beetle we can get about 5 mpg. We need the enclosed trailer because we put the Harley in front, but we sometimes tow a stacked trailer that adds another 9000 lbs. If we travel out West we plan on taking the stacked trailer so we can take the toys. That drops the mileage to 3-4 which is where the S60 would maybe help with its torque. I would like to see what a 40' prevost S60 pulling a stacked trailer gets for mileage.