Will pellets draw moisture if stored outdoors (in bags, in a storage tub, on a covered deck)??
Not much. The only precaution I ever take is when I have a bag that is torn, open, or has a hole it it I make sure it is in the pool storage box or an old garden can with a lid that I have. As long as the bag is well sealed the pellets will stay fine. I have one or two bags of a pellet "flavor" I don't use much that are probably six or seven years old and have been kept stacked on a concrete floor in an area where direct rain or snow won't hit them. They're fine. Just being exposed to ambient air of normal humidity won't hurt pellets.
Pellets remaining in the hoppers of my cookers stay there until the next use. I don't scoop them out and bag them back up. Sometimes it may be a month or more between uses depending on what I'm cooking. No problems there, either.
Hub