I know I was concerned about the wall in front of my torch, but to be honest with you, I have put my hand on that back wall after torching for 3 or more hours, and it's not even warm. And neither is my hood. I run a scorpion and I run it full out a lot of the time, I know there are lot bigger torches out there that create more heat than mine, but I think with the ventilation that I have most of the heat goes out and the vents at the back of my bench keep things cool back there. For my setup, any air gaps would just be overkill, not really necessary .
here are some old, old pics of my set up:
This is while my studio was being built, so nothing is finished.
But you should get the idea. I have a 900cfm granger squirrel cage fan.