The BASIX assessment and NatHERS process is an ever evolving practice which requires extensive knowledge of available materials, passive heating and cooling strategies and how to design in an ecologically sustainable manner. Although to complete and sign off on the BASIX process one must be a certified assessor. The assessor’s background does not play a large role in determining their competency in assessing a building’s efficiency. Therefore, the question is raised as to who is the most qualified or most knowledgeable to be completing the BASIX assessment?

You really need to check with the council. 
While not particularly a ‘relocatable home’ as it sounds like an existing residence, not a new prefab one, this is the only information on the BASIX website:

Prior to commencing most types of developments in NSW, you will have to lodge a Development Application (DA) with your local council. 

BASIX (Building Sustainability Index) assesses the energy and water efficiency of your development. It is one of the most important planning tools currently operating in NSW to ensure buildings are being developed to operate in a sustainable manner. In NSW the State Government requires that a BASIX Certificate is attached to all development plans when submitted for DA approval.

The $500 million Indigenous Infrastructure Investment Fund (IIIF) allocated to both Aboriginal and Torres Strait Islander groups can be used not only to increase their economic participation, but also promote sustainability in critical resources they have no or limited access to. In this article, we will dig deep into how the funding can be used to promote sustainability in Indigenous communities.

Obtaining a Building Sustainability Index (BASIX) certificate is vital in the development application process in New South Wales and is applicable to all new residential dwelling types. This sustainable, water-efficient, and energy-saving measure is strictly implemented to those who are building a new home.

Earlier this year a structural engineer in Darwin was caught out on building design as it deemed to be considered non-compliant with the National Construction Code. The engineer was rightfully suspended of his engineering registration by the Northern Territory's Department of Infrastructure, Planning and Logistics (DPIL).

With New South Wales currently going through a drought, now is the best time to find out ways of increasing water efficiency for your next residential project. This helps in working towards a BASIX certificate, here are five ways that you can design a water efficient home: