I had a '69 camper with all the camping options several years ago (RIP) and the
front "hammock" was really a canvas "stretcher" which fit over the front seats.
The sides of the stretcher were two steel poles the ends of which fit into
brackets which mounted on the bus pillars. It was only big enough for a small
(very) adult or child but convenient for storing gear off the floor while
camping. I never had anyone actually sleep in one so I don't know how
comfortable they are for that purpose.
Tim Schlaile  '87 Vanagon Camper