So I managed to find a solution.
Had to replace my C:\openHAB\userdata\etc\org.ops4j.pax.logging.cfg with one that contains only:
org.ops4j.pax.logging.log4j2.config.file=${karaf.etc}/log4j2.xml
Then added the following to my log4j2.xml
<!-- GPSTracker appender -->
<RollingRandomAccessFile append="true" fileName="${sys:openhab.logdir}/gpstracker.log" filePattern="${sys:openhab.logdir}/gpstracker.log.%i" immediateFlush="true" name="GPSTRACKER">
<PatternLayout>
<Pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%-5.5p] [%-50.50c] - %m%n</Pattern>
</PatternLayout>
<Policies>
<SizeBasedTriggeringPolicy size="16 MB"/>
</Policies>
<DefaultRolloverStrategy max="8"/>
</RollingRandomAccessFile>
<!-- GPS Tracker -->
<Logger additivity="false" level="TRACE" name="org.openhab.binding.gpstracker">
<AppenderRef ref="GPSTRACKER"/>
</Logger>
Hope this helps someone else.
Mark