In my case when I transfered my rego to Vic I only had to have an adress where the van was to suppose to be garaged and a letter from the owner to say that they knew me.
It seems from my own personal experience this week, the staff pf the SA Transport office are not very familiar with the services their department provides. That said, I believe you only have to show you've been in the state for a short time to the Dept of Transport office near you. You may have to have the vehicle inspected at the Regency Park Transport Dept. I needed a certificate of roadworthy for Rosy, but the Transport Dept staff didn't know what I was talking about. It turned out I had to go to the RAA to get it. All good. Go to the site and send your question on the contact form. They do respond. Good luck with that.
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20ft Roma caravan - Mercedes Benz Sprinter - SA-based at the moment. Transport has no borders.
Management makes the decisions, but is not affected by the decisions it makes.