Please be careful about using non-food-grade plastic for fermentation and proofing. Many non food-grade plastics contain nasty compounds that can be absorbed by your dough. You have no way of knowing the extent of this risk. I wouldn't take the gamble.
I will look into this. I can't imagine that the extent of leeching, if any, in the absence of heating/microwaving, etc. would cause any ill effects. If you, or anyone else has any specific info (especially to the contrary!) that you could shoot my way I'd appreciate it.
Additionally, the "food grade" containers that I've purchased are "almost perfect" in terms of fitting in the fridge, but not quite... I'll continue the search
I am not really sure what "food grade" plastic is, in fact. Does it refer to the chemicals used, ability to resist scratching, ability to not harbor bacterial colonies???
It is important for people to know that I am not recommending these as a commercial solution.