That's excellent mpg, a little more beleivable than the guy who claimed to get 36mpg towing with a large 4x4, We had a 1.9 diesel sharan which, solo was about the most economical large mpv on the market. If we drove it solo at caravanning speeds 50 mpg was easily acheivable on a run but put our 20' ta caravan on the back and it was down to 25-27 mpg, 30 if you really tried.
When driving solo a large percentage of the engines output is used to simply turn the engine hence a small engine is best but when towing, more power is used to pull the vehicle along so the small engine becomes little better than a much larger engine