In reply to anonymous123:
The sevel vans (Citroen relay, Peugeot boxer, Fiat Ducato) are also worth considering. I'm still on my first van - my initial thoughts were a transit, but after a bit of research decided the sevel shape was better for converting and living in (widest in class and pretty square walls), and otherwise they were pretty similar - both reliable, cheap to buy, and high availability of spare parts wherever you're traveling.
As long as you get the 2006-on model, rust shouldn't be a problem (I made that mistake with a 2004 so have had some rust to deal with) as it'll have a galvanised chassis.
Also, don't worry too much about higher mileage, age and condition is more important - a young high mileage van means it's been driving up and down motorways all day every day, which they're well suited for. Expect the engines to go well north of 200,000 if they've been serviced and looked after.