let me clarify why I mentioned sawdust, fresh milled sawdust usually will have a water content drier than the air, it will hungry for water, it will want to stabilize to the air it is in, so if you moisten it and seal it in a bag, after a week inside the bag it will be dry. Try throw some sawdust in some water and see how long it takes to completely saturate with water.
Sawdust is the opposite of a good packing substrate, use paper towels, coco coir, peat moss, or even paper or cardboard, anything is better. Sawdust will suck out all the moisture, so when you shipped me those seeds they started moist, started sprouting, then dried out and died. $30 is equivalent to my monthly water bill here.