Where do you live? What kind of quantity in terms of tonnage are you talking? What type of feed? I try not to keep my sweet feed around that long in order to keep it fresh but there again it depends on how much you are thinking about keeping. I have used feed wagons in the past which hold about 3 or so tons at a time but I feed it within a couple of weeks. It's inside a barn and the flys can be a problem. I have just purchased several upright poly-bulk bins, the 3.5 ton size, with augers. That way I can see how much feed is actually left in the bin and it will stop the fly issues. I chose poly because there are no ridges/seams to catch feed. I think that it really depends on how cold your environment gets and how much feed/type you are planning on keeping for that long.