I used Adobe Illustrator and some images of Transit vans to work out my basic design and layout. It was not perfect, but by making them roughly to-scale, I could work out basic estimations for material needs and spaces required for furniture units.
The side profile turned out to be fairly accurate in terms of what I built. The only error was not realising that the seats project back in to the van so I had less space than first imagined. It also meant that I put the shelf over the bulk head (to make space for the seats).
By making a roughly to scale version of my van I could plan a lot of the practicalities before I had even bought the van.
On the below design, the pink dotted lines on the image below show the approximate workings for how the fabric panels and cupboards will work.
As you can see, not everything I designed I included into the design. Especially in this back-view!
Some parts changed based on practicalities for the build and others because, once you can see things coming together, it is clear that some ideas on paper do not quite work as well in practice.
The top view shows the basic simplicity of the design I was aiming for. In reality nothing is nearly as simple as it looks – but the end result does feel reasonably uncomplicated.
As you can see I was counting on the ability to store most of my things either beside the bed (clothes and personal effects) or under the bed (everything else). Also worth mentioning that there is handy storage over the cab, and under the chair too.