I saw the module sold on DX and others.
Yes it's cheap, but you get what you pay for.
It's to be powered 5VDC not 12 for the ones I checked.
I also had a look at the HR202 humidity sensor, and between 10 and 15˚C, you have around 20% resistor variation. 4.0K to 4.7K
This means that if you change the temperature of the cave, the humidity will not read correctly anymore, until you set it again.
Concerning the potentiometer, you have to set it, wait 5-10 seconds and check if it's ok. Else, turn a little more or less, wait and check again.
Something more reliable with no need of external power, digital, in a box and is around 15 euros.
Search for WH8040 on ebay or else.
There are some things you don't want to be on the very cheap side if you do not want to ruin your cheeses
Bon, je parle aussi français hein ! Je suis juste un immigré au pays des caribous.