I've been using a SWB 1.3 Doblo for the past 5 years and get around 39 to 40mpg - this is in South West Wales on twisty, hilly routes with a 350L tank, ladder plus other kit.
Had to replace alternator, glow plugs & top mounts in the last year but at 7 years old/70,000 miles I guess that's not too bad. In hindsight I wish I'd gone for the 1.6 LWB for a little extra power & space but all in all quite happy with the van & I'll probably keep it until it goes no more.