Hi:
I thought I would chime in with some info.
RainSongs will not have a problem with humidity extremes. The instrument can get wet and the carbon/graphite integrity will not be harmed (obviously, electronics, tuners, strings etc. are exceptions).
The instrument is unaffected by freezing temperatures. One of our Dealers (Colorado) left one outside in the snow overnight and played it the next morning as a "test". (He is no longer a RainSong Dealer
)
As far a extreme heat is concerned, I guess it comes down to the definition of "extreme". In our early stages of production, we had some faulty resin systems that could not tolerate high temperatures. In the instruments that we have built for the last 10 years, we have not had a single complaint about heat-related damage (knock on wood
). So, I would say that a RainSong stored in a case in a car should be fine.
I hope this helps.
Ashvin