This is coming from a former museum collections professional -
Climate Controled is going to be your best best, you want humidity 55%+/-3%, mold is more likely to grow above 60% (You can get a cheap hydrothermograph on amazon, they’re close enough for what you need). If the facility tends to run humid then think about a desiccant but they have a finite use life and you won’t be there to monitor when to replace, you don’t want to just dump a bunch in there at once either. I’m comfortable enough with the residential type that I store my wooden and textile family antiques at one (with a tyvex floor and top covers as well as pig mat snakes around the edge)
Make sure each piece is cushioned/supported, I’ve worked with some gnarly old leather pieces that just collapsed on themselves
Very, very conservatively condition the pieces before storage, you don’t want a thick coat or it can congeal but you also want to protect it from seasonal humidity swings (most residential commercial storage facilities still swing because of the outside world and trust me you don’t want to pay to store with an art handler $$$ )
If you really want to read up, AIC put together a list of leather care resources https://www.connectingtocollections.org/leatherandfur/ (technically how the items were tanned can effect storage too but for 2 years of storage for items I assume are in active use, it should be fine without)
Also- check to see if your property insurance covers items in rental units, I believe USAA’s is kind of picky
