You need to do an inspection of the bottom of your unit. Find any access for air and close it up. I noticed on my unit that the storage area is directly connected in two locations to the inside. A floor vent in the bathroom and a vent under the steps. Any warm moist air getting into that storage area will condense when it touches colder surfaces. Make sure all access doors to the storage are closed.
After that you might want to check your air conditioners to make sure the coils are clean. It's not hard to do. Go up on the roof and remove a few screws to get the cover off. You can buy a can of coil cleaner at wallyworld. If the coils are covered with gunk they will hold moisture instead of shedding it. Check the inside part of the unit also. Also make sure your drains are clear so the water can get away from the a/c.
If none of that gets you anywhere, I would look at a dehumidifier before a heater. It will remove water. The problem is it will also generate heat.