Verified answer

The basic rule of thumb is that your guitar should never be in a place where you would be uncomfortable being yourself.

That may be unavoidable, but you can mitigate some of the potenoutial harm by burying the case under a lot of other stuff that will insulate it from high temepratures (clothes and sleeping bags, pillows, etc., work well) or keep it in the passenger area (out of the sun) with the AC on.

Paint can chip, finishes can craze or bubble, and even worse, the neck can warp (the tension rod in the neck is metal and it can get seriously tweaked at high enough temperatures).

Other than heat, extereme cold can cause just as much damage, and you must absolutely keep it out of the rain. A little moisture is okay (in fact getting too dry can wreck the tonal quality of the wood), but getting drenched will RUIN the thing.

My best advice is to tune down your strings all loose! If you travel by plane, the best you can do is to remove the strings, as the pressure in the sky may affect the strings.. even make them break the neck if your really unfortunate. I wouldn't worry to much about the paint get chipped off, I think if you are comfortable with the temperature your guitar is as well

I do not know if electric guitars have the same problems as acoustic guitars and violins. I know that I do not leave by guitar and my violin in really hot places (over 120) or really gold places (under 32) because that increases the risk of cracks. Sudden changes in humidity also increase the risk of cracks. Hope that information helps.

take it on board, dont check it