I bet a cheap PVC pipe or Hvac tube with a single fan is all you need for cooling.
My trouble is how to keep noise out my theater because I want the rack mounted flush into my side wall, but I want sound isolation and low noise floor. I love seeing the equipment inside the theater look. But cutting holes in your walls messes up your sound proofing. Much harder to cut holes and install fans for cooling when you are also chasing sound proofing.