Many marinas ban the use of unattended heaters. I know mine does. Plus, heat could make mildew worse (unless it burns your boat down first
Installing a device that condenses the water and dumps it in your galley sink is about a simple as it gest. I'm not sure that your suggestion of evaporating water into the air is any simpler or more effective.
I'm with Take Five on this, and have done quite a bit of testing.
* Heater (light bulb only lowers the humidity in the immediate area, and only if the amount of ventilation is just right (too much and the heat goes away). For this to be effective it would have to be enough to warm the boat 5-10F to allow for distribution problems. 60w is not enough for most boats. I used bulbs in the past and effectiveness was mixed (good near the bulb, not far away, 27-foot boat).
* Any water evaporated can easily re-condense in a cooler portion of the boat (under a mattress or in a locker against the hull, for example). This is the bane of boats that are heated and occupied.
* The power consumption is the same.
* RH will be lowered about 5 times further by a dehumidifier than a bulb. Tested it.
Is this overkill? Everything depends on the climate, size of the boat, leakage and usage. My boat is a little larger, sees some winter use, and is in a damp place. I do know that a dehumidifier will keep the bedding fresh through the winter, and ventilation, well, not so much.
There with be a PS article out on this soon.
Sail Delmarva: Dehumidifier vs Desicant
CaCl2 is a total waste of time unless the boat can be PERFECTLY sealed, or unless many large containers are used. They remove pathetically little in low temperatures.