I recall reading about how that Ansel Adams thought that it was unwise for camera cases to be black. He did an experiment in which he painted one white. Comparing it to a black one, he found that the white one heated up much more slowly than the black one.
I suppose that a white case, or an aluminum one, with thick styrofoam liner inside, might be a good choice for protecting optical instruments from heat, for a while at least. The aluminum by itself may reflect radiation some, but keep in mind that aluminum is also a good conductor of ambient heat (like in frying pans, radiators, and air conditioner heat exchangers, etc.). It needs an insulating material between itself and the protected interior to keep oven-like heat from transferring rapidly from outside to inside.
Taking the camera with you is probably a better idea yet.