I found that adding a dehumidifier to my Cal 40 kept our boat dry, light and mildew free. After a long day of sailing i can put wet gear including a soaked spinnaker down below and come back the next day and everything is DRY.
Step 1: Buy a Dehumidifier
You need to get a special unit that has an attachment for an external drain. This enables you to route the drain to the bildge so you can run the unit all the time. I bought a ComfortAire for around $130 at my local hardware store. You will also need a 5ft garden hose to attach to the unit. Each unit may vary so check and make sure to get the proper hose for your unit.