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No support is required, and in fact none should be used since it would be difficult to remove from inside the duct.
I recommend using a high-temp PLA for this fan duct--the type that is dishwasher safe--just to ensure that it won't warp or sag over time. I added some Kapton tape and aluminum foil tape to protect it from the heater block, but I'm not sure if that's necessary. I've used mine for over a year on many prints with no problems. You should cover the screw holes with some foil tape so that no air leaks out, although that may not be absolutely necessary.
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