In this van, the owner has built in a bunk with storage underneath. It also has some nice features including a skylight, fridge, and plenty of storage, along with a divider between the living area and cab. which allow the space to be heated or cooled easier.
This is an example of an easy solution to using the back of your van as a sleeping quarters. The plywood can be folded out into a platform for sleeping when their is no cargo, and folded back up and put away to make room for cargo.
This van has a built in bunk with storage underneath and a plywood sub floor. It also has an inverter and LED lighting for energy efficiency.
Read more about customizing your van at thread on building van beds
The next two images include folding bed options for vans.
This is a DIY bunk based on an Airstream design. It could be a great option for a van owner that wants to build a small sleeping bunk.
Do it yourself RV projects like the one pictured above
There are quite a few of these caravans still out on the roads. They are dependable, and with the four cylinder option, fuel efficient.
This Astro Van pictures shows the different options available to a DIY van build. This Astro van incorporated a folding bed/ kitchen table design usually seen in small pull behind campers.
Link to photo