Is there a calculator that can approximate the expected MPG

10 mpg is a good ballpark number. That's if you hold your speed to 60 and don't have a significant headwind. I've seen as low as 7 and as high as 14. But for budget purposes, we work with 10 mpg.

No there isn't. 10 is about the norm, some as little as 6, 12 if your pulling a popup. The weight of the TT doesn't matter as much as the speed you travel and the "frontal area". A larger TT then the one you have now won't make much difference unless it is a 5er with a larger frontal area.

There are far too many variables to easily calculate this. Average is 10. I get 10 with my current combo. I previously towed this trailer with a 2003 Trailblazer and I got 8. The same Trailblazer with a 17 ft hybrid and I got 11.

Try dividing the gasoline used into the miles driven using an old school adding machine. Works every time.

I use calculator...miles divided by gallons, each fillup. At end of trip total miles div. By gallons for trip average. Gas 2500, Avg 9.5, towing only..gas motorhome, Ford V-10 always seemed to be 8.0. Doesn't seem to matter uphill, downhill. Tail wind will give a tad better on a fillup, headwind wind a little less. Speed 55-60.

OP,what are you trying to accomplish? You've been around here long enough to know that RVing isn't an MPG friendly hobby. So curious as to why you are asking.

There are too many variables for even the same truck and same trailer to get the same mpg driving on the same road, when driven by different drivers. The driver has alot to do with the mpg. Then start trying to compare completely different trucks, trailers, roads and drivers all together and that's just a big mess that you really can't get any reliable data from.

We just did 7500 miles and averaged 10.7 about half of it in the Rockies. That's derived from gallons bought and odometer miles.

You can expect over 6mpg and less than 16mpg.

Down load the smart phone app, gas logger. Works great to give you cost and MPG for each fill up.