Turning green is caused by exposure to light. Be sure to exclude light
from the sacks. Farmers round here do main crop potato picking around
October so as long as you keep the tubs dry you'll probably be OK until
then. In fact if you don't need the tubs until next spring why not
consider them as your storage system, particularly if you can keep them
protected from frost. If you have a lid for the tubs pop them up on
bricks to let moisture drain, pop the lid on then lift potatoes out as
and when you need them.