Surprised no one has chimed in. I get 17-19 with our
Scamp 13, so I'd expect a bit less, maybe 14-17 with a Parkliner. My '11 Pilot has the older 5-speed automatic; the newer transmissions in the 2016+ models might be a little more efficient.
But really, so many factors affect towing mileage- terrain, weather, driving style, cargo load, rooftop gear- that I don't put too much stock in reported figures, nor do I care much. Even most full timers drive far more miles unhitched than hitched, and we only take 3-4 trips a year within the Southwest. I'm more concerned that the vehicle is able to pull the
weight with acceptable performance and long-term durability.
On the other hand, non-towing fuel mileage matters a lot to me as I drive 25K miles a year, about half work related. I get 25-26 mpg on rural 2-lanes at 55-65 mph that constitute the bulk of my driving. Overall about 22-23 mpg over the course of a year, including about 2K towing.
If you really want the best mileage possible, change your driving style, not your vehicle. Slow down, avoid strong headwinds, use the right gear for the grade... did I say slow down?
Or buy a diesel. If you put on 20K or more actual towing miles a year it might be worth it. The Jeep Grand Cherokee has a diesel option, I believe.