thats an interresting thread .. i´m goin to ask my luthier what he has to say about this. i personally have never had a problem with humidity. at least not to an extent where the guitars get out of tune. infact i dont have to retune my guitars at all even after weeks. the temperature in the room where my guitars are fluctuates between 25-28 C in summer to 21-24 C in winter. but most of the time it is about 23 C. outside the temp varies from 50°C to -25°C