@mpous yes I think it is working now - I have gateway_key.bin in the the right place and if I do the command:
/usr/bin/helium_gateway -c /etc/helium_gateway/ key info
I get returned my key, onboarding and name with expected details.
Thanks for all your help 
Just FYI, for anyone finding this in the future, if you update the hm-pyhelper version in the packet forwarder container to the latest and use the VARIANT panther-fl1 or pisces-fl1 you should be able to get it to work on reset pin 16 / GPIO23 (should also work with COMP-PANTHERX1 or COMP-PISCESP100).
You can see the pin mapping at… hm-pyhelper/hardware_definitions.py at master · NebraLtd/hm-pyhelper · GitHub