Obstruction between the Mezuzah and the Doorpost
Question
Is there a problem with wrapping the Mezuzah in plastic, as it creates an obstruction between the Mezuzah and the doorpost?
Answer
Shalom!
The opinion of the Shulchan Aruch is that one should place the Mezuzah inside a tube or some other covering before affixing it to the doorpost, and this does not constitute an obstruction. This is the common custom among the majority of Jewish communities, wherever they may be.
However, in the name of the Gaon of Vilna, it is brought down that it is forbidden to wrap the Mezuzah, and it should be placed on the doorpost as it is, so that there is no obstruction between the Mezuzah and the doorpost. [This is the custom in the house of Brisk].
Source
Shulchan Aruch, section Yoreh Deah, chapter 289, paragraph 1, and see there in Pitchei