A combination of the two following changes have got it working:
1. Created the _promaps_geocache.xml file with the example XML you provided as a starting point.
2. Changed permissions for folder and file to '777' (read/write all).
However, the created XML has ![CDATA] tags throughout. What would cause this? And is this an issue?
<?xml version="1.0" encoding="utf-8"?>
<geocode_entry ID="200 George Street Sydney NSW 2000 Australia"><address><![CDATA[200 George Street, Sydney, NSW, 2000, Australia]]></address><geocode><![CDATA[(-33.862622, 151.207813)]]></geocode></geocode_entry></geocode_data>