I think that's a good plan, Mary Stella. The soil you use will act as an insulator and temperature moderator. Barely moist would be optimal, and if the bulbs get slightly dehydrated, that will increase their resistance to freezing . As long as the box doesn't receive direct sun, in a plastic bag would be fine. Unless you actually know for sure what the temperature is like in an unheated shed throughout the winter, don't use it. Sometimes sheds can get amazingly warm with the sun beating down on them in the early spring.
If you keep the Uchida bulb in your ca. 50°F crawlspace, do not water the soil until you are ready for it to begin growing. This will help delay premature sprouting.
