Storing dry grain - I wouldn't worry. FWIW I pickup up a 5 gallon food grade bucket at HD today - about $4. I needed it for wet curing in the dorm fridge.
When Food Babe was about 3 I fermented more than a few batches in a plastic trash container with a plastic bag from the cleaners for the lid. Turned out good enough for what we were brewing then.
Monks used to ferment beer in a thing made of rocks