Stop in for a cup of coffee

Our car club has 2 containers but we have a bit of a moisture problem, have to address that this spring
Only way have ever seen that removed is either roof vent that is motorized But that relly depends on the outside humidity level. or a dehumidifier. Thats what I will use and plumb the drain out. Run it once a week a few hours and every time I open it up and close it. Military has the same issue.