As said, there is nothing wrong with towing on OD, but it doesn't mean it has to be the best way.
I did tow a trailer with a vehicle that had trip computer showing instant mpg.
Having 5 speed auto -I was playing with it being bored driving with low speed limit in CA.
On some occasions dropping a gear was bringing increase in mpg -also giving much better response when I needed it. Following tall semi could give me 15% increase, but that is tiring.