...why not cut a small hole in your Air conditioning duct (...) and shunt a small tube onto the cage.

Because 1) That's going to WAY too much trouble, and 2) in the winter, you'd be blasting heat onto the cage.

I don't think you have anything to worry about, temperature-wise. These laptop hard drives are meant to run fairly warm. And on the Mark 1's at least, they aren't stacked atop each other, they're side by side, so they don't burn each other up too badly.

Although cooling is required for some kinds of hard disks. I once had a file server with multiple full-size 7200-rpm drives stacked directly atop each other. It took several months of continuous use before they burned up... Make sure your file servers have fans on their hard drives...

Tony Fabris
Empeg #144