Do you not have have air-con? I'm also in Australia (just over the mountain from you!
IMO decoraters that don't have access to air-con are seriously hampered in our summer.
A ganached cake once set properly can be covered in fondant and will be fine if temps are 23-25degrees
MOST Australians have air conditioning, even if it is only 1 room, 99.9% of cars are air-conditioned and depending on the choice of venue.... MOST of those are air-conditioned too.
I know a...