Hi John,
Congratulations on your decision to emigrate to Australia, and
to I.I.S
Brisbane can be a humid place, especially in the warmer months.
I know the setup you have is BIG AND HEAVY, but I wouldn't leave a scope for an extended period of time covered over, your biggest threats would be mould growth on your mirrors and depending where you live, THEFT!!
Remember, the U.K. sent ALL their convicts out here.
Either break the unit down after use or put up the observatory, QUICK!!.
Cheers, John.