My Dad built a set of bunks like that for his 65 chevy van when we moved back to the continental US from Alaska in 68. They were plywood and hung from chains. I slept over the cab, like the one shown here, my sister slept just behind the front seats. Mom & dad slept on a dinette unit Dad made in the back.
We camped from Western Canada to the Dakotas until there was an issue with a defective propane bottle in a portable heater. Mom got burned, the van didn't, but we never camped in it again either.