Sorry I don't know the addon you mention. Here is some additional information about how to install the linuxserver/plex container on the command line https://hub.docker.com/r/linuxserver/plex vía SSH.
Thanks for the link. I was able to get my local mount successfully added to plex and confirmed that it is retained after a restart.
You set the paths in the addon settings. Keep in mind that the remote paths should already be mounted and you use the local mount point.
I did try it first from the web ui. If I understood it correctly, only folders within the plex container were available to be added as library along with the default host folders for movie, tv and pictures. As I mentioned in my original post, the NAS is already mounted under /storag/NAS, however this was not visible.
I was able to get the mount point added with a new install of plex using the cli commands for the link provided by elonesna.