This is quite a specific question, as most RAK2245 boards are combined with a Raspberry Pi. In this case you can use the ChirpStack Gateway OS already which comes pre-configured with the Concentratord.
However, I am planning to add more documentation about Concentratord. Currently I’m doing quite a bit of refactoring to support multi-downlink support (https://github.com/brocaar/chirpstack-network-server/commit/8ad3f71d6048b6ad6b5c6d73c4f071b3914f7653 + https://github.com/brocaar/chirpstack-gateway-bridge/commit/463423ef309cb731ffdabfaba57a6d7d03d2bfb6) which I also want to make part of Concentratord, before releasing it as “stable” + some other tidying up 
I am also planning to provide packages for various gateway brands and models.