Kev, that is not entirely right. Water vapour is less of a problem for seeing. It is mainly the laminaire flow which is important for seeing. Water vapour can create clouds and that does disturb seeing, but it is less important than mountain ranges and terrain issues.
So Far Anthony and I have found a couple of sites. First and foremost is Exmouth WA. Highest level of seeing experienced by either of us yet, not been there myself but I have seen the video. We think though that Broome could be better yet. One of us was going to go there this year, but it cannot happen now. Next eyar perhaps.
Next, Clayton Bay SA. I have had DIM (seeing meter) results from there with long periods of 0.7" and an average of 1" seeing. I have done a few planetary imaging tests from there (
see here) but yet to try in earnest. For DSO imaging though it has been a great spot. 1" seeing generally and the results have been quite sharp I think. Dark sky town too. Perhaps we all ought to setup there. Plenty of land for sale. Clouds can a problem though.
Murrembateman is also good too. Anthony's images from his home very good and he has a good record of the seeing conditions there. Perhaps contact him and ask his opinion.
Seeing at Broken Hill is also good. Trevor Barry's images attest to that. The problem though is that seeing can be inconsitent. I am sure Trevor will be able to tell you more about that. Heat during summer could well be an issue too.
Arkaroola has potential too. Seeing in winter can be sub arc but summer it is crap. The heat plumes are a nightmare from what I have seen and heard. Been up there in summer and the seeing was quite bad.
I suspect that in the far north the seeing would be quite good too. There is little jet stream influence and Cairns are would have quite laminair flow most of the time. When I lived there I noted sea breezes dominate the air flow. Although cloud becomes a significant problem for this region.
Flow straight off the ocean though is what you generally need. If the flow dominates like that then you are onto something. You cannot have any intervening mountain structures as this kills seeing by virtue of eddies forming.