So here's what I have been working on for my van.
It will eventually be a side facing bench seat which extends to become a double bed.
I forgot to take the before pics, but I will describe the process, I started with the frame from a double bed which I cut in half, I then cut out about 2" from one of the halfs so it would fit inside the other. I then riveted some fully extending rails between the two halfs so that the frame can extend from half width to full width.
I still have to attach some wood to the slats which slide out to stop the frame over extending.
Below are the pics of it's current build state.
Extended
Detail of one of the rails
Showing how the frame will hinge up to allow access to the storage. The white frame is part of a second bed frame which I am using to make the base.
Being the cheap b*****d I am, both the frames I have used have been free. Check out your local freecycle site for people chucking metal bed frames.