I cold smoked a few things in my mini with my homemade tube smoker and noticed the same, about a 20-25 degree rise over ambient temp. I think I remember reading that the original Amazn smoker using dust puts out less heat, so maybe as the weather warms that might be the way to go. I like the frozen water bottle idea too.
It does put out less heat. I will try it too.
I have the dust smoker, pellet smoker, 6 in. tube and 12 in. tube.