SSAA Insurance Brokers' standard Contents insurance covers contents items temporarily removed, for up to 35 days in any premium year, anywhere in the world. The coverage in Oz/NZ may not have the 35 day limitation, but the policy wording's a bit ambiguous here.

There are some exclusions, to do with leisure vehicles and surfboards etc when not in a building, but firearms are not affected, as long as they're not being used as 'tools of trade'.

For firearms not specifically listed in a policy schedule, with valuations etc, the claim limits are $1500 per item, $10000 total.

The difficult bit with doubles would be getting a realistic valuation. Only the few shops that have a bit of a DR speciality [e.g. McDonald's and Century Arms, and maybe Whitehorse Arms, of the Melbourne lot] would know their values well enough.