Air warms during the day and rises, vents are vital so that the warm, damp air has a way out. Non vented plastic or waterproof covers trap moisture in and do much more damage than good. Covers also need support which allows no puddling on the cover. Quality boat covers made from materials such as Sunbrella® or Sharkskin® can have additional vents added and pole type supports.
These easy preventative measures will help ensure a fun season on the water for years to come.