The colors fade (especially with Ektachrome) and fungus can grow on the gelatin emulsion side of the slides. So when I moved to Brazil around 1978 I bought a refrigerator; now I have two of them (I regularly throw away images that I know will never sell to make more room). The older refrigerator never needed repair (except for replacing the door seal twice), it still uses that prohibited gas (chlorofluorocarbon (CFC =Freon). The second one lasted just a few years and had to be replaced. Power consumption is low as I do not open them often. The humidity condenses on the freezer so the air around the pictures is dry (I use strips of humidity indicator paper (with cobalt chloride?) which are pink while in a humid environment but turn blue when dry) (I bought mine from Hydrion about 30 years ago but I see it still exists: Micro Essential Laboratory; also: Taylor Scientific . Slides are placed in 20-slide sleeves, several of which in turn are placed in paper envelopes. I retrieve envelopes placing them quickly in plastic garbage bags (a blue one on the photograph), then in a second bag to incresease humidity protection. I open the bags only after several hours when the slides are at ambient temperature.
Both retrieving an envelope or placing it back has to be fast as not to let much humidity enter the refrigerator, so sometimes to place envelopes back I choose the first empty space I see, and my file becomes fragmented like a hard disk…
The only problem is when there is a power failure, not uncommon here. For up to 3 or 4 hours there is no problem, but if it lasts longer than that the ice starts melting and water falls on the envelopes containing the slide sheets. On a couple of time I had to spread plastic slide sheets all over my apartment to dry.
When ice accumulates on the freezer I need to de-freeze. I remove the envelopes from the top shelf, and I place a thick layer of towels to absorb the water that falls outside the collecting drawer. The older refrigerator has no auto-defrost, so have to leave it open. I hopefully somewhat protect the items in the inside of the door and in the main compartment by hanging towels in front of them.