Hi!
I always have my travelling guitar (a spanish classical) with me on tour. I strap it to the right side of the rear rack in a hard case, and in hot weather keep the neck covered by tying my towel around it (good for drying the towel out as well). When it rains I just put it in two bin liners.
This I have done a lot in temperatures up to 40 C and never had problems with warping. Had a bridge come off once after long usage but I couldn't tell you specifically what caused the glue to dry out...
I am cautious leaving the guitar in a closed tent in blaring sunlight. I leave the case open and cover it with a sarong.
My travelling guitars are $200 ones, not my $2000 guitars
so they're "replaceable" however much I love them
Here's a picture of my rig... you can just make out the guitar on the far side covered with a towel in the heat of a Portugal summer.