Or to answer this a different way, fuel mileage is sooo subjective to begin with multitudes of factors that make direct comparisons not practical. Not the least of which are driving habits, locale, vehicle, size of camper, “optimistic” reports by fuel mileage “kings” etc.
A generic “10ft camper” could range from a popup to a Host or Eagle Cap. And that alone will make a huge difference.
If you’re thinking about a TC for fuel savings only, it’s not likely going to pan out as well as one might hope.