Plenty of mining flights have occurred over the years to non aid, non forecast aerodromes with no planned alternate. Given that CASA, mining companies, and the ATSB haven't said anything, which includes several high level incidents, I think it is safe to say that all you need is a GAF and use LSALT +500 for your weather and you can't do it at night if you are >5700KG.
I'm sure if you nearly crashed an aeroplane the ATSB would make mention that you didn't have a legal forecast.