I would recommend getting a 3+ ton van as anything less will be be borderline over payload when fully loaded with water etc. I have a transit mwb which is wide enough to mount the waste tank behind the TM to save space which is handy, not sure that would be possible in Vivaro size vans. Transits will start to rust from 5 years old however.
I am about to purchase a new van and I think I'm going to go for a Crafter, I would like a Transporter but think I would regret the lack of space, shame as the sportline in black looks awesome.
Jamie