never in view. always in the boot if i have to leave it in the car - and put it in the boot before u get to your destination or else you're just shouting out to everyone that u have a dSLR waiting to be stolen in your boot.
Electronics die faster in high temperatures, and sensors have VERY fine electronics. I have been told by Fujifilm specifically that heat is quite a killer. I recommend that you don't keep your cameras in a hot place (like a car in the hot sun) or place your dry cabinet on the wall with direct afternoon sun.