Hi Honey eater. I'm in the Perth Hills also, and have Flow Hives.
I have small vents in the lid, probably smaller than the standard ones on the Migratory tops common around here. Seems to keep condensation under control.
The other hive I have is traditional lang with no plastic frames. The bees sealed up the vents, and have less condensation issues on that one.
I don't know whether the plastic flow frames, being less absorbent, get more condensation on them, or just a fluke.