Rema Orach Chaim 135:1 permits one to move a sefer torah to be used in a jail as long as it placed there a day or two before it is used.
I have a recollection of a custom to require a plan to read from a sefer torah at least three times in a new 'temporary' location (e.g. a shivah house) in order to allow it to be moved there.
Does such a custom exist, and what is its source?