"iTunes media folder location" keeps reverting to local storage instead of persisting the NAS location, how to stop this?
Put the iTunes itl file on the NAS along with the media.  Then lock the copy of the file that's in your $HOME.
Launch iTunes.
iTunes will whine that it can't open the library (it thinks it needs to write to it), and will ask you for another.
Point it at the one on the NAS.
Now, iTunes will regularly, as you know, try to revert back to the one under $HOME.  But now it can't, so if it does, you get the prompt, and can redirect it.
Instead of discovering some time later after it's been storing media on the local drive again.