Bratface
Contributor
If it's out of sunlight it will be fine, heat or no heat. Inside a suitcase won't have any higher ambient temperature than the rest of the garage so there's no "extra heat" to be had by storing it where it will remain clean and easily kept together.
I'm really amazed at all the fuss people make about their gear. The purpose is to get it wet, it's not going to melt in the rain or even in the heat. UV and chemicals are about the only thing that's going to damage gear being stored. It will last a lifetime if you protect it from those two things.
I have to disagree with fjpatrum. When you have spent several thousand dollars on gear there is a big fuss to be made about storing/caring for gear. I dive in salt water and want to keep the bladder of my BC rinsed as well as rinsing my gear thoroughly. I want to dry it so that it won't mildew or smell, and I want to keep it serviced regularly so that it will not fail me.
Personally, I keep some stuff at the house and some at the dive shop where I am a regular and I service my regulator annually and protect my mask from damage by keeping it in the box when it's not in use.