Solve the high humidity problem in your basement. Is it humid outside? Are the windows open? Do you have water leaking in through the walls or floor? Are the ducts insulated?

I agree with ionized. I had a very slight issue with humidity in the basement and plan to eventually finish it. I solved my issue by adding a supply vent on one end of the house and a return on the other in the basement which moves enough air around to keep things under control. You will need more than just some airflow. I would check into adding a dehumidifier and searching and reducing the sources if possible.