Photos of my bed conversion in my 2003 Cruiser Avan. (As result of a request by Helen A.)
The original setup of folding base changing between sofa and bed, was a pain, because the base hinged-folds made it too hard to get to the stuff under the bed. And it was impossible without removing the mattress.
So I replaced the hinged base with a solid piece of 12mm thick ply cut to size (and varnished). The top angle and bottom timber strengthener at the front, and the hinge at the rear, were all transferred from the old base to the new base.
Gas struts from Bunnings competed the job, allowing the bed to be lifted with mattress and bedding n place, the struts holding up the bed.
To support the bottom ends of the struts, I added pieces of ply, screw to existing timber supports under the bed.
The struts were bought from Bunnings, and are marked 400N. I tried lower pressure units, but they didn't hold the bed up.