Sack-Ups work great!
I'd wipe down of course any firearms, extra barrels and the like before inserting.
Cut a long rifle into, now you have two Sack-ups, for extra barrels. How we kept our barrels for barrel sets fine and dandy in all sorts of conditions, for extended times. We keep handguns, spare mags, and the like in these too.
Put it this way, off site I have some stuff, I have not bothered to even mess with in a year - wiped down and in Sack-Ups.
I normally use RIG when I do this extended storage bit - did not have time, and to be honest, based on past history doing this - not going to worry about. *shrug*
Actually I am getting a kick out of a few folks going bonkers, that I really am not worried, don't care and someday 'Maybe I'll check on that stuff".
Free Cigar boxes are great for sticking smaller hand guns in, mags and the like.