We don't often pull boats very far with it, but Mary and I have a 1990 Honda Civic that gets 49 mpg around town. We used to go to regattas in the early 80s with a VW Rabbit PU with a cap and it got 60mpg. But pulling the Hobie 18 it was hard to get it in high gear unless drafting behind a truck.
Going north to our summer home last spring, Mary was pulling 3 Waves with the Honda Odyssy and got 30 mpg.

The RV gets 10 mpg diesel fuel no matter what it is pulling.
Not enought to warrant staying away from a regatta.
Rick