I can't sing the praises of the "Vittles Vault" made by Gamma Squared (
http://www.gamma2.net/) nearly loudly enough for this application. I bought one of these for dog food (its intended purpose) and was loading it into the truck when the light came on and I went back into the store and bought them out (and subsequently ordered more from the manufacturer). The key is the screw on lid and O-ring which make a moisture and insect tight seal and I've never had a rodent knaw through one. I've found forgotton ones full of grain in the basement and found the grain fresh and sweet smelling and capable of producing wort after 5 years (I didn't have the cujones to make beer with that wort though). One of the normal size ones will hold a 25 kg sack of grain and there are smaller sized which can be used if you store specialty grains in smaller quantities (or used to send your pooch off for boarding for a couple of days).
With the gamma seal lid storage in a dry place is no longer so important (though more moisture will naturally find its way into the headspace if you open the container in a humid location) but it is still best to keep grain cool. Note that these things are stackable and they now make one with a side opening so you ought to be able to tuck them into a corner somewhere in the brewery or garage.