Dave
Is your intended new van expected to do the same as your current one or carry a bigger payload?
For example, if you are running a porty now and want to carry a rotary, CRB, along with the associated accessories that go with them, then any of the machines will fulfill your needs.
But if you are thinking that you may go for a T/M within the next 12 months, for example, or maybe auxilliary tanks for a van-mounted porty, and you want to use the same van, then you'll have a whole lot of new considerations to take on board, especially weights.
What about parking? I have a Citroen Dispatch and this will go into a multi storey cark park no problem. I don't know about the Vivaro.
Safe and happy cleaning
The Ken