I wish we lived closer and I could hire you to convert one for me...I’ve been looking at the Ford Transit Courier for this purpose. It is the smallest of any I have see. In Moncton the Post Office uses them for local pick-up and delivery of mail. It is built on the Ford Focus chassis so it is more like a car with a tall roof than a van. It comes in different models, the delivery models have no windows in the back but there are others with windows all around and even some built originally as campers.