This is a remixed version of the fan duct mod published here by Nexi-Tech.
I increased the thickness of the bolt stand-offs as I was finding the originals to be a bit too thin and would easily break due to accidental over tightening of the mounting bolts (the stock fan duct suffers the same issue). This is a far more robust design and the stock bolts are plenty long enough to accommodate.
No supports are needed for this model (although I did print mine with a skirt)
I've printed this at both 0.1 and 0.2 resolution, and either version looks and works perfectly fine.
I've also printed this at 20% infill and 100% infill. I prefer the 100% as it adds a greater level of strength to the part while only adding a small amount of time to the overall print.