Storing root crops buried in sand-filled containers is a great way to keep them crisp in a cold cellar, and I prefer metal for this. You can certainly use a food-grade plastic container, but my concern is about what we now consider “food-grade”. There’s mounting evidence to show that some kinds of plastics powerfully mimic the action of female hormones in the human body. At the moment this is only a concern for certain types of plastic, but our knowledge is limited. Rather than try to figure out which plastics are safe and which are not, I prefer to keep stored food away from plastics as much as possible. This is the thinking behind root storage in galvanized metal garbage cans when used with sand. Using this method I’ve successfully stored beets for more than a year in my root cellar.