Brian from Owen Sound, Ontario has passed on his tip for keeping cold rooms cold.
He simply brings in a 4 inch duct from outdoors high up on one side of the room and points it toward the floor. On the other end of the room he brings in a second duct in the same fashion but locates this one at the floor. The flow of air between the two tends to keep the room cold.
I think that is a good start, but cold rooms are always tricky to keep at the right temperature all year long. If it tends to get too cold I will usually apply a half to one inch of foam insulation to the ceiling ? the ceiling being the area of greatest heat loss as it is usually the concrete porch that is over the cold room. I would also put dampers on both of Brian's ducts, just to give you some control over the air flow if you find you need it. And as an insurance policy against freezing all your food stock, I put a 500 watt baseboard heater in the room and set the thermostat at just above freezing. Hopefully it will never go on, but if necessary it will save things from freezing.