I was in college for 3 years with a few guns that were stored in hard cases any time I was at school, and not shooting. This was in northern NY, in an unheated storage unit, and the guns (except on organized trap events) never even saw a heated building, or normally any type of cleaning.
Guess what? They are fine. Wipe down with an oily rag, or one of the silicone rags, and call it good.
Is it the best? No, but then again I'm riding around without a speedometer right now because my daily ride puked up it's speedo cable. (at least I hope that is all that is wrong) I still need to get to work, however I still ride the bike, and I deal with something not being perfect.
That said, right now the guns are leaning up in the closet, with the two I have use for in HD loaded.
::EDIT:: As for storing them in the storage unit, There was no way I was storing guns outside of some sort of case, as they shared tight quarters with all kinds of things, from spare tires/wheels, tools, bulky things, and even an ironing board, way to much crowding and gunk to leave guns uncased.