Payload should be your 1st consideration, even with a 350l tank. The most common payload for a small van is around 600kg, but though in theory, that should work fine, in practice, it would be touch and go!. I have a lwb transit connect with a 900kg payload, but a recent run over a customers weigh bridge gave me a bit of a shock. With a full 500l tank, she was tipping the scales at 2300kg, only 40kg less than my gvw!. And no, I don't carry heaps of other stuff in my van!. So, if you can, go for the higher payload versions of whatever small van you choose.