Prolonged low humidity for acoustics is always a concern, but overall, I think quality built instruments can take more cold/heat than you'd think. As long as it isn't a sudden massive change in temp, and as long as it doesn't stay in extreme low or high temps for Very long periods of time. Countless touring acts since the touring profession existed have had their gear in the non climate controlled storage holds under buses, in planes, in trailers, vans, trunks of cars...you name it. Not to mention, playing outdoor summertime shows where it's already 100 degrees out...then add 10 more from the hot stage lights! During my years as a tour mgr, our stage gear which was in a box trailer pulled behind a bus, which included everything from acoustics, electrics, upright bass, Hammond B3, drums, full percussion rig, etc......it all stayed in hotel parking lots in -20 degrees F to 105 degrees F.... countless times!! (10 straight yrs of playing 250-300 gigs a year!! Southern beaches in the summer, northern ski resorts in the winter.) Never once did we worry about the gear. Just as long as it was all inside the club to gradually acclimate several hours before showtime. Never had a single structural issue with anything. Mechanical/electrical...regularly. Never structural.
Tom, I'd say just don't ever let them get too dry....or experience sudden extreme temp changes. Otherwise, I'd bet they'll be just fine.
