For this application I always recommend the Vittles Vault,
http://www.gamma2.net/, designed for pet food (and accordingly sold at many pet stores) but perfect for malt. And whenever I am asked I always tell of how I found a forgotten one five years after it was placed there in my dank basement and how the
grain still smelled fresh and sweet and converted nicely (though I didn't dare use it an actual beer). The secret is that the lid screws into the container and there is an o-ring which makes a vapor, bug, rodent proof seal.
They come in several configurations and sizes. The most useful holds a 55 lb sack of malt with room to spare. They stack and there are ones that can be opened from the side (so you can get
grain out of the one on the bottom of the stack without having to take others off.