Do you have a restaurant supply house nearby? If so, they should have big food-grade sealed containers that are perfect for storing grain. If not, I've heard of folks going to the pet store and getting those big sealed bins that you use to store dog food.
I empty bags of grain into Homer buckets. One 55lb sack will fill up just a little more than 2 buckets.
I store unopened bags in large Sterilite latch totes from Home Depot. I think they are 36 gallon or something and cost about $11 or $12 each. Each tote will hold three 55lb sacks of grain.
Storing unopened bags in totes is probably unnecessary, but I think it looks cleaner and gives me a little peace of mind that it would be harder for rodents to get to them.