I have recently investigated this myself.
Two out of three gas fitters (recommended by various people for marine work) do not know or understand the gas standards NZS 5601 part 2.
For an installation like yours with a single appliance, you are allowed to use flexible hose to NZS 1869 Class C, which for the layman is standard BBQ hose, costs $12/m at Burnsco and costs the gas fitters $4/m.
Two of the gas fitters claimed for that single appliance install I needed copper hose with flexible stainless steel at each end. The additional cost was several thousand dollars. Additionally t