Prevention is best. When a house is heated unevenly (like no heat in bathroom), mold tends to grow.
Adding heat did not raise the electric bill much, because the bathroom fan was not needed as much, because of less condensation after the heater was installed.
Keep areas free and clear, for air ventilation. Mold likes to grow behind things that are close to walls.
Those little pots of pellet dessicant to work. That's why hotel rooms keep them in the room. 5 of those for $5 can do a small room for a long time, maybe a year. When the pot fills with water, you know it did its job and then discard it. Don't try to remove the paper filter on the top because its purpose is to prevent water from spilling if the pot gets knocked over. Also, the paper keeps pets from drinking the combo of water and melted dessicant.