Thought I would share the bed/ sofa system I recently built for my Chevy Express van. After lurking for a bit, I got the idea for the Ikea Exarby sofabed from saabman. I built a subframe for it out of superstrut (home depot unistrut). It secures in the van via the oem pin system for the rear bench seat. The subframe allows for additional storage space underneath the bed and allows for it to be removable. Two castors at the rear of the frame help to level it and makes it easier to get it in and out of the garage.
The following shows how the bed is attached to the strut. They are brackets designed for attaching conduit to the strut, looks like they were designed for my purpose. The bed frame slides on the subframe to allow for clearance at the side of the van when the bed is flat.
The following shows the connection for the oem seat system. I used two superstrut angles that had 1/2 holes (same size as the oem pins). I had to grind the angles a bit to allow the holes to line up (shortened them). The sofa bed is fairly well secured, I think it would stay put in an accident, but comes out easily by pulling the two pins.
Hopes that helps someone if they are looking to do something similar.