importing a caravan from usa

And most exceed the maximum width of 2500mm, especially if they have a roll out awning attached.
OJ

Size is no problem, he is only going to use it on his own block.

However it will be considered as a "transportable structure or vehicle." It will therefore have to conform to AS/NZS 3001 - Electrical installations - Transportable structures and vehicles including their site supplies. You could also get around that problem by only using a 12 V system in it. You could do that by using a solar system or a mains driven 12 V system driven by the mains located externally to the van. A 240/110 V step down transformer is not an option, AS 3001 does not allow it.

Then there is the gas problem. The Yanks use steel pipes. That is not allowed here. None of the gas appliances will have Oz approval numbers, they will have to be removed.

There was a report in one of the newsgroups from a bloke who tried to change state registration. His 5th wheeler was over width so it was knocked back. Then when it came to using it as a static van he had to spend heaps removing the gas installation.

Also read through Importing Vehicles to Australia -including reading the link to VSB-10.

Don't start your importing until you have all the facts, you could be blowing your money.