This is where it stands at the moment.

Looks like the extension that turns the above into a bed should just be a bit of board that drop into side gutters, and then just add foam?
Be interested to see any pictures or plans that anyone has or hear any experience from camping life.
Other advice such as measurements, best foam or board type to make this complete all very welcome. Doesn't look to be more than 2 or 3 inches clearance between base and roof once the top is down
Also puzzled how you get up into these roofs once bed is extended, do the boards stop short of the front and you clamber in through the gap towards the driver's end, or do you get up then slide the boards? Having never seen one complete or in action, a bit hard to picture. Please enlighten me..

May also be tempted to just put foam on what is there and sleep kids up top, but would need to fashion some sort of guard to prevent them from diving onto those below in the dead of night. Anyone come up with a solution for that? Problem seems to be a gate could only clamp to the bottom as rest is canvas and not sure it would be strong enough...