I guess it depends on your definition of long term. From my perspective, 6-7 months isn't long term given that those months are cold (relatively) here on the Maine coast. In addition, during our cold months the absolute amount of water vapor in the air is much smaller than in summer. I would definitely empty the tank if the storage was going to be multi-year or possibly even for a 6-7 months in a hot climate like CT, or NY or places further south