We recently purchased a 16” HiLo, towed it from PA to CO with a 2006 Honda Ridgeline (5k tow capacity).
My unloaded MPG on a cruise like that is about 20-22 mpg.
Towing a conventional 17’ box camper I get 12mpg, and feel every passing vehicle and breeze.
The Hilo we ranged from 16 to 18, on cruise at 60-65mph. Best part was big rigs passing us at 80 mph and we never felt a thing.
Having towed a number of conventional boxes, you can really feel the drag when you hit about 45mph. The hilo feels the same up to cruising speed - just a load, not a sudden wall at 45.