Oiling it well, putting a gun in a silicone impregnated sock and then in the hard case should be ok for quite awhile.
Depends on what you mean by long term.
From my own experience, up to a year, even in a humid part of the country, will be agreeable this way.
Walt Kelly, alias Pogo, sez:
“Don't take life so serious, son, it ain't nohow permanent.”