Music into itunes on an external drive

Been having a few problems getting Hazel to add files to itunes. The folder it is called 'Music Library' on an external drive.
I need to do the following:
Add any files added to Muisc Library in the last hour to itunes.
I have tried various combinations, but they all seem to produce unwanted side effects - Missing some deeply nested files or copying files into the iTunes library more than once so that it gets filled with duplicates (Seems to be something to do with the fact its an external drive).
Please can you give me a bullet proof set of rules to get this done.
Many thanks.
I need to do the following:
Add any files added to Muisc Library in the last hour to itunes.
I have tried various combinations, but they all seem to produce unwanted side effects - Missing some deeply nested files or copying files into the iTunes library more than once so that it gets filled with duplicates (Seems to be something to do with the fact its an external drive).
Please can you give me a bullet proof set of rules to get this done.
Many thanks.