I've seen folks have good luck with those large tupperware type storage bins. They just toss the bags in there, as many as will fit, and put the lid on and tuck them under a pool table or in a corner somewhere, and they seem fine. We are talking whole grains right? and not ones that have been ground. I've kept ground (or "cracked") grains for probably a lot longer than the brewsites and manufacturers recommend, but I've never had any trouble as long as I kept the mice out of it. I stored some cracked pale malt grains in the shipping back for 3 months before using them, and I couldn't tell any difference in the final outcome. They were kept inside, in controlled temps (~ 71°F) and in a dark place.
I wish I had the storage space for bulk storage, and the need for brewing that much to warrant it. *sigh* I'll just have to keep ordering my grains as I need them and hope nothing comes up in RL that prevents me from using them in time before they go bad. I think I'd cry if I had to throw out 16# of cracked grains. Just cry..