Just wanted to answer the OP's questions about the heater adding to the moisture. A major product of combustion is water
vapor, so if your heater is burning anything and not properly vented outside, then yes it is adding moisture. Electric
heat, or heat with a functioning exhaust
should not add moisture.
As a mechanical engineer
, the ventilation suggestions sound good, and I'm intrigued by a manufacturer saying night ventilation is better because the water
vapor has fallen out of the air as dew and therefore the air you bring in is drier.