There seems to be a common practice of using simple heat sources for dehumidification. (for tropical climates at least, I guess excess moisture is less of a problem in temperate climates)
Eg. fixing an always-on lamp inside wardrobes, and various cabinets which are non-airtight. For protecting clothing or electrical equipment from moisture damage.
I can imagine that when the lamp is first turned on, the interior temperature increases until the heat loss rate equals the lamp power. Relative humidity drops accordingly until the temperature stabilizes. At this stage, this should not be controversial.
But I do not expect the low-RH to be sustainable, given that the cabinet is not air-tight or moisture tight. My intuition is that moisture would migrate into the heated cabinet until the RH is equalized inside and out. Is this correct?
Another possibility is that water vapor tends to spread so that absolute humidity is equalized...
So what is the relevant theory of humidity?
(I am not talking about electrical "dry-boxes" marketed for storing cameras and lenses, those I'm sure have a way of pumping out moisture, and those are practically air-tight. I am talking about a low-tech heater-in-cabinet arrangement.)