That's pretty reasonable, considering the weight & bulk. We can just get our Vito up to 30 mpg on a long trip, provided we don't go too mad on the autobahn The Vito is almost certainly lighter and has the smaller V6 engine, but of course (like the GL) its height and width makes it considerably more 'draggy' at motorway speeds than a normal vehicle.I think if I were able to demontrate more throttle restraint and the bits at either end of the Motorway bit weren't so fiddly then 30mpg is possible.
Typical consumption is about the same as you reported ... 25-26 mpg.