what's the best load luggers with economy

My van weighs 1650 kg's fully laden so going on a 3 week jaunt to spain needs a load lugger with lots of space and good power to weight ratio to get up and down them french and spanish mountains,problem is the last time we went we spent £1,000.00 on fuel & tolls, 800 on fuel, 200 on tolls average mpg from 17 to 22. Is there a good load lugger that gives better economy that still has plenty of grunt, I have been looking at volvo V70 d5 auto, but don't know what it would return towing my van