Lot of effort. Unless it was a Sandman van to begin with you might as well just buy a van in the first place and avoid rego issues and all that.

I reckon if I was going to that effort I'd take a wagon and graft on the panelvan turret/sides/upper tailgate to create a 4 door , 5 seat , ultimate family panelvan. Wagon rear seat folds flat to the floor so you could still have a decent load space, sleeping area when needed.