we've done it already for internal customers and process itself is not very complex. But obviously depends on a scale.
First of all, same instructions apply as to standalone installations. So, if you have an Installation Guide - you are already on a way.
Dockerizing DB part will be the most tricky one, as you have to use/manage Docker volumes for data dir of postgres.
Then, it's about taking postgres image (Docker Hub or your own), putting desired config (postgresql.conf, pg_hba.conf, etc), creating schema(s) for PRPC, installing PLJava (I'm pretty sure it's still a must), installing PRPC using standard installation tools.
When that's done - remember, there is a volume out there on your host system, which has to be managed. You can either pack it and distribute, or use volume plugins (such as Flocker).
App server part is quite trivial. One thing only - you will need to link it with DB, obviously. Docker provides that feature, called --link or --add-hosts.
Once app server can reach DB instance - you're good to configure JDBC connection string and credentials. Configurations can be put in into image during build or mounted during startup of container.
And, generally speaking, this is it. Hope that gives you direction. Feel free to drop further questions.