Mpg has many variables,
We get better mpg when on flattish roads with little traffic to hold you up, tail winds, and driving at a steady speed around 60mph, motor up to operating temperature.
When driving on hilly roads, high speeds or into headwinds , motor not up to operating temperature, mpg will be nowhere near as high.
Because someone posts they got 50mpg it doesn't mean that they get it every trip, only when conditions were favorable. Don't forget a T6 van weighs between 2-3 Ton depending on load., campervan conversion etc.