I expect you will need a "garaging address" for the vehicle in NSW.
The seller may allow you to use theirs.
Cheers,
Peter

Would be cheaper to have dealer register it to your WA address. That would also apply to Insurance premiums as well.

An inspection by the WA authorities may be required before they allow WA registration. That is certainly the requirement in SA.
Re-registering in the current state of rego is typically easy by comparison.
Why would WA rego and insurance be cheaper?
Cheers,
Peter

I purchased my first van in Victoria and brought it back to NSW. The dealer removed the plates and affixed a notice on the door glass and I had I think about 28 days to get an inspection and register in NSW. I would suggest you contact your local motor registry and follow their instructions as it would be something that happens regularly.

Motor dealers may register a new vehicle in any State - As to why Stamp Duty, Insurances etc are cheaper in WA, SA or Qld - Who knows the machinations of State Governments?

Advantages of an initial registration in OP's home State is; Not having to get annual inspections, these can be difficult when vehicle is not in NSW,

It also obviates the necessity of "Blue slip" (or WA equivalent) full inspections, when he returns home.

Vehicle will be easier to sell in State where registered - assuming he will not sell before he gets home.

Thank you people.
All true. Of course the permit for 28 days would be necessary to drive from Sydney to Perth, but not to continue going North.
Maybe try to use dealers address to register in NSW or just drive it home.
Either way your efforts are appreciated.
As for stamp duty...6% in WA but mh classified as heavy vehicle is 3%.

We had a van built in Melbourne and tried to get it licensed in Victoria so that we could dawdle on our way home to Perth. We could not do that unless we had a Victorian address. The dealership had to supply Vicroads with our address and could not use theirs. So we tried getting plates from WA prior to our travelling across to pick up the van, but no, even though it was a new van, they want to inspect it in WA before registration. Told the only way to bring it back was on a movement permit of which we could get a maximum 14 days which put payed to any real holiday on the way home. We did that blissfully unaware that the Victorian movement permit is valid in every state except WA, you need to also obtain a WA one for your travels in WA. So our van, unknown to us was unregistered for the last part of our journey. In the old days, we regularly bought a Viscount in Sydney and did a trip around the east coast with the van on NSW plates until we got home, but it seems in recent years they have put paid to that. The only way around it is if you have friends in the state you buy from and use their address, but that can be risky as all your other licences are from WA and police computers are now interlinked across states. They consider your vehicle unregistered if you residence is in another State. Gets very messy.

What do international visitors do? Those who fly in, buy a vehicle and travel the country for a year or something? They would not have a residential address anywhere in the country.

When I bought my first van the dealer suggested that I book in at the local caravan park and he would include that as my address and the plates would then remain on the van. I chose the travel permit as I was coming back to NSW. I think the issue with temporary addresses is more about your driving licence and insurance declarations.

Many thanks to all who offered suggestions.
We got fed up w the whole stupid thing and bought a new Iluka here in WA.
Problem solved!!!