If you’re stuck on bootstrapping with the proxy method, I’ve had good success with the cached install method that requires no internet at all on the machine you’re installing on: How to install Discourse on an isolated CentOS 7 server
It works the same on any linux distribution that can run a recent version of docker.
I recommend creating a shell script for the git clone steps to save a lot of time when it’s time to update the caches, and to make sure you update everything at the same time.
It quickly becomes a mess if you forget to keep all your plugins in sync with the base discourse.