Hi Richard
I ran across this photo in a Paul Hamlyn P/L book, Camping and Caravans, published in 1973. It has about 35 pages on caravanning, lots of general information and some photos.
The only information published with this photo reads; "Sedan based motor vans are rare in Australia but some miniature caravans have been built from discarded Holden bodies. Cheap to acquire and light to tow, these bodies make excellent supplementary camping space."
Circumstances have changed a bit since 1973 as far as availability and prices for old Holdens go maybe, but if you have a spare one lying about this might be the go for a project
Maybe this one is still lurking in a shed waiting to be discovered
George