motor roamin

Is any got any figures on 40ft diesel pusher with 400 Cummins ?
It's a truck so expect worst 8 and best 10mpg but thats loaded and towing also doesn't make much difference if it's a 330 or 425hp they will be between that on a 40' best I had was a 300 in a 34' could achieve 15 but more often than not it was 12, must admit I never think about the diesel so long as there is enough in the tank then I'm off and going where ever it takes me (y)