This little item for Holden's Motor Body Builders indicates they exhibited at the first NRMA Camping and Caravan show and it's the only item I've managed to find so far from the first show.
They exhibited their camping body conversion, better than sleeping on a park bench I suppose. My 1961 Vauxhall has a similar set up but I've never even tried it.
And another item from Pointers magazine showing the set up in more detail.
George