Buy a van that can hold a decent tank, 650 at least. It takes a while to make 3-400 last all day and you have the tank capacity to work longer etc when you do get experienced. My one big regret was getting a doblo that can only carry a 400 litre tank and even then, the garage said the bump stops are wearing out from the suspension bottoming out.
So, van with a tonne payload (boxer,hiace, transit, etc) and 650 litre system.