All of the Radiant Australia towel rails are rated either IPX4 or IPX5 when hard wired. The AS/NZS wiring regulations permit for IPX4 or greater rating appliances to be installed in zone 1 of your bathroom (which includes above baths and at the end of open showers). They must be hard-wired and the controller/switch must be positioned in zone 3.
You electrician can find details of this in their Australian Electrican Standards book on page 249 of AS/NZS 3000:2007 or on page 323 of AS/NZS 3000:2018.
As bathroom designs vary greatly and as with any electrical appliance, please ask your builder to consult the current version of the AS/NZS 3000 electrical regulations and any relevant local authority / inspector in order to confirm the exact position allowable.