From the article: "Conservatively, it looks like about 1100 miles per gallon for DEF fluid."
My experience so far is that I can go from here to Houston, TX and back on a single 2.5 gallon jug. That's about 1280 mpg. I don't track it, so it's just an approximation, but I've done the trip a few times and it seems to hold close enough. That's about 1 gallon of DEF per 80 gallons of diesel, in my case at least.
The Delano is wider and maybe taller and almost certainly heavier than my Class B van (I'm about a ton under the GVWR of 11,030 lb), so I would expect a bit lower mileage, but I would still expect to see somewhere around 1000 mpg. These things are real DEF, and fuel for that matter, sippers.
Tom & Jeri
2018 Coachmen Galleria 24T Li3