I suppose the original idea was seeing ute-trays used as trailer tubs. A ute tray is much the same shape as the section of kombi I used, except that the chassis and suspension is built into the kombi. The kombi is pretty straight sided and the height was about right, so it made a lot of sense. I think if I were to tackle it again I would use a ute tray and build a chassis for it underneath. Trying to convert a kombi was pretty difficult.