Well, I've spent the night trawling Australian forums (nothing much else to do - house is empty and being recarpeted tomorrow!)
I've changed plans a bit, the first change is to go from a sleeper like I've started above to a wooden base, much lower than previously planned. I have a 3rd row seat (which may be for sale soon for a cash injection into this bed project!). And plan to use the 2nd row folded down as my foot area when sleeping so that the frame can stay in the truck and just be a 5 seater with "storage" bins. Given my truck has the fridge it will be a little different from this one.
Source:
http://www.patrol4x4.com/forum/diy-modifications-accessories-40/sleeping-gq-72175/Hey guys, Yesterday I setup the back of the Q to fit a double blow up mattress.
the base is 1100mm square and about 150 high. lines up heightwise pretty well with the wheel arches and the 2nd row seats when folded down. the surface is made of masonite. (Its looking really strong but i gess time will tell)
It fits snug between the arches so its not moving anywhere when 4wding but can be removed from the car in less than a 1 min if needed.
when not in use, the 2nd row seats are compeltely useable and the rear slat of masonite lifts out (located by dowels) and slips into the middle drawer so the base can be used to store eskys, snatchys etc!
Quick, easy, cheap and suits its purpose perfectly!