I have always heard of acoustic guitars being sensitive to heat, but what about solid body guitars/basses etc.?
The neck can warp, but I don't think the body changes. That is, if you have that thick poly. All I know is my black pj gets hot in the summer sun.
I don't mean specifically in the sun as in direct sunlight, I just mean high temps in general.....90 to 105 degrees. Figure in it's case and in a car or in a room on a hot day.
Never leave an instrument in any conditions where you yourself would be uncomfortable. If you would be OK, likely your instrument will be OK. Hot cars destroy instruments--btw a car in the sun will easily get over 140 F. http://www.injuryprevention.org/states/la/hotcars/hotcars.htm