I have been buying base malts (mostly Pilsner and Marris Otter) in 55 lb. sacks and it takes me about a year to go through a sack of each. I’m storing them (loose) in pet food containers https://www.amazon.com/IRIS-Airtight-Food-Container-Quarts/dp/B00186RTWW/ref=zg_bs_2975354011_20/181-4447006-4316514 . They claim to be airtight but I doubt it’s 100%.
I’ve been throwing a couple 100 gm sachets of silica gel in each container. Is this a good thing to do? Bad thing? Not necessary? Not enough?
You’ve been doing it for at least a year…how’s it working?
Well, silica gel doesn’t seem to be hurting anything.
Not sure about the silica gel, but I do pretty much the same thing with the same grains. I use Rubbermaid storage containers at about 50-70F with humidity at about 50%. I have been doing it for years and no perceivable problems.
Doubt you need the silica unless your house is really humid.
Yeah, I’m not sure about the need for the silica gel either. That’s why I’m asking. I’ve been going with it because of my home brewer’s obsessive/compulsive streak.
Nope, this is semi-desert. Though, right now it’s cold/wet/snowy/sloppy here. And we are all very tired of it! 
I use vitles vaults from Amazon. They work ok but it did notice that when I buy a new sack of grain that it is more crunchy than the older grain in the bin. I want to say that the grain in the bin is 6-7 months old. It could be summer humidity but I haven’t noticed a change in the performance of the grain in brewing. I also recently listened to a podcast called experimental homebrewing and they had people reportedly brewing with uncrushed grains that were 18 months old with no off flavors. I also read in BYO Magazine that the storage time varies by grain type and the largest change noted was with speciality malts.
I also keep sacks of pils and MO, but I just keep them in the original bags and twist the top closed and put a weight on it. I also put them in a big Rubbermaid bin, but that is more about mice than freshness. I keep them in my basement, so 50-70F and 50% humidity.
My reasoning is that if that bag is good enough to ship/store it in for the company, it should be good enough for my purposes as long as I can reasonably close it.
They seem to last for the 9 months or so that it takes me to use them up. When I had them somewhere that the humidity went up to 80% there was a noticeable lack of crunch after a few months. Not spongy, but not super crisp either.
I used to use the same container as you to store my grains but I felt it didnt seal that well either. I never had any problems with them, but I switched over to vittle vaults because they seem to seal better. Whether or not they are better, I have no idea. BTW besides amazon, I have seen vittle vaults at TJMaxx or Marshalls for pretty cheap. As far as the silica packs, dont eat them 
The gel packs have a limited reaction time and can only absorb so much oxygen. I’d save my money and not use them unless packing grain into smaller quantities that will be used once opened.