We have a rather old large galvanized metal feed storage bin. Its about 5 feet wide by maybe 3 or 4 foot deep and 3 foot tall (very approx sizes- will measure it if anyone is interested). We don't really use it any more, we tend to use plastic barrels to store feeding in instead, plus the goat shed we have now isn't so convienent for propping open the lid when using it.
It has a hinged lid, with hasp so you could padlock it. It can easily take 8 25kg bags of feeding, and I think we often squeezed in 10. We've had it ever since I can remember, so probably for at least 25 years, but its still strong and sturdy.
I've had a look at new ones on the web, and they are all much smaller and far more flimsy.
If anyone is interested, please let me know. We are near Falkirk, so Central Scotland. It can be lifted by 2 people- though its easier with 3 as then the third person can hold up the lid so it doesn't squish your hands! We moved it originally in our 6 by 4 foot Ifor williams livestock trailer. We could probably deliver if you wanted.
Beth