Just an update - since July in Orlando we have had high 90 degree weather and a close hurricane scrape. It usually thunder storms every afternoon which increases the already high humidity (which usually gives us heat indexes in the 105 range).
Never bought the cover and leave my pellets in the hopper on my garaged Bull and no issues. It does get some dust on the outside which I can live with.
Maybe down the road if the cover goes on sale I will grab one, but for now the Bull naked has been fine.