I currently keep both my dog and my cat food in 5 gallon buckets with gamma seal lids. Keeps for months, no problem. Easier for this old lady to handle than those big barrels, especially when it gets close to the bottom of the barrel and I can't reach the bottom easily and can't lift it either and so end up pretty much standing on my head in the barrel to scoop! LOL
But I currently have a 75 pound rhodesian ridgeback and she goes through a lot of dog food so I am thinking of doing the barrel thing again like I did for y2k, just because of the way prices are going up, up up, up and how we may be getting closer to a supply chain disruption.
For y2k, I used 55 gallon food grade hard plastic barrels with screw top lids. They had olives in them before I got them. I washed them good, then aired them for a couple weeks. Then I simply used dessicant (in coffee filters) and just filled them up with dog food and a dessicant pouch every so often (about 2 or 3 to a 50 pound bag IIRC) and then screwed the lid on tight. I didn't even caulk the lids.
I stored them outsie on my deck for a year (100 degree plus in summer, low teens in the winter) and it all did just fine. No rodents tried to eat through it or anything and no bears came after it (which was my biggest concern). The food did not go rancid or get buggy and my girl ate it just fine without any ill effects. I do think it was a little stale towards the end, or maybe had the sent of greek olives, I don't know, but you could tell she was not impressed by the end. LOL But she ate it!
3 barrels lasted 9 months, but YMMV of course. Of course, I do like many others here and supplement the dry food with home cooked food (rice, vegies, occasional meat, some leftovers) so it goes farther and has better nutrition (and flavor!)
I would think that with dessicant to keep the moisture down you should be fine. Of course I do not live in a high humidity area either, but common sense says to store it however you store rice or grains in a high humidity area.