Welcome to the forum Mr Democracy.
Yes, under the regs you can install a safe in the apartment. Needs to be bolted down (drilling concrete is noisy) unless it weighs 150 kg or more. Buy one bigger than u think u need. A 6 gun safe will most likely only hold 3 or 4 at most.
Neighbours should not even know your installing a safe. (Security wise, I don't advertise) Does the building owner need to know, do you need permission? That could be problematic.
Rifles in public places like elevators is problematic. I would use a case that does not make it obvious. Then say its a musical instrument if asked by a neighbour.
In Vic you generally get an inspection shortly after your first gun purchase.
Here:
https://www.police.vic.gov.au/safe-storage
The greatest invention in the history of man is beer.
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Member. SFFP, Shooters Union.
SSAA, the powerful gun lobby.
Hunt safe.