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.