This document will attempt to assit with helping you to understand how to create a subfolder that you can access via a panel iframe component. Using this method, you should be able to access Hass.io addons from outside of your home network.
I will assume you already have the NGINX addon up and running on HASSOS.
I will use Node-RED as the target URL for this example....so I will also assume you have that addon installed and running too.