I understand the current Docker image has been conceived as a portable installation tool, so every setup is up-to-date, but this choice makes the image kinda useless for those who live behind corporate proxies/firewalls.
Please consider releasing a ready-to-use image (post-install) where particular settings can be provided at run time (actually this is how most images are usually set).
I think your best bet is to put the server in a VLAN where it can accept and make connections to the corporate net, and only make connections to outside.
This is required for, e.g. embedding Wikipedia and checking image sizes.
docker save + docker load from a DMZ doesn’t actually help enough here, because the migrations need read/write access to the database.