I think we are going to take the plunge and get something like a Vivaro/trafic/Primastar. Ideally set up with bed and stuff. Been looking on EBay, Gumtree and Pre-loved but there’s not loads about. Where else should I be looking?

Either DIY or pay a premium because someone has already done it.

what’s the budget?

Simon,
You’ve seen our vivaro at Malham last yr, we’ve had ours 5 yrs now and it’s a DIY. Used for race meetings and holidays (regular weeks and overnights with 2 bikes) I would be cautious buying someone else’s DIY unless very sure of the build, much better to buy a decent base vehicle and add to it yourself. Get it perfect for you, loads of ideas on the net. Doesn’t have to cost a fortune to self build. Wouldn’t be without it now.
Peter

Me and my son have just bought a van and are half way through converting it into a day van, a lot of the converted vans out there aren’t well set up for cycling. if you go down this route you will be looking at van+ around grand or so, no stove/fridge/vents/toilet but bike store/ ply lined fabric trimmed/insulated/ beds/ electrics etc.
Bit of graft involved but you get exactly the build you want 😉