CJ
My 6.7 Cummins gets 7-8 MPG at 70MPH.
Slow down to 60 or below, jumps to 10-11MPG.
Same with Jason's Duramax.
This is towing my 232 Gulfstream,10,100 lbs.
I still say 3/4 or more to pull a Seafarer. Mine, back when I had it, weighed 6000 or so, depending on how full the tank was and...