For as long as I can remember I have had to adjust my insulin dosages and reduce my dosages when hot weather arrives. This partly due to the increased level of activity during warmer weather, but I am convinced that the hot weather itself lowers my need for insulin. In the late fall I have to start increasing my dosages again. These dosage adjustments are not all that much, but they are important.
When out and about, on a hot day, I carry my insulin vial without any cooling device.I have done that for many years and the insulin has never been affected by the heat, I always keep the insulin out of direct sunlight.