The school bus conversion is pretty easy. This COE has a custom body behind it. Ford built these as cab-chassis units for other manufacturers to add bodies to. This example looks modern; but I wouldn't bet high on that. The beauty of the COE is minimum vehicle length. When you get into camper rigs this is important if you get off paved roads and need room for sleeping quarters plus a little extra for gear, cooking, etc.

Plus the smaller, lighter vehicle keeps costs down. And then there is the advantage of engineering this kind of body on to a conventional pickup with all the common parts that such an approach offers. The extra 2-3 feet of payload space gained by moving the driver forward counts for a lot. So why not just a van conversion and be like everyone else? For a lot of us that question answers itself. I'll never get another van, myself (hard to work on).