I tried to fit stock E3D v5 hotend fan assembly under Reinforced Prusa X Carriage with Slim LM8UU Holder without much success. There is simply not enough space between the LM8UU holders. Therefore I designed this duct/holder, which connects to the 15x10x10mm accessory mount point on the carriage, and allows to suck away excess heat from the hotend's heatsink. Since the fan is further from the heatsink, it is less efficient. Still, I tested cooling from 200deg.C to 60deg.C with and without the fan running, and the cooling time is 4 and 8 minutes respectively. So this arrangement is still ok, efficiency-wise. I printed this with 0.35 layers, 0.4 nozzle, and it turned out ok. You may need to reduce the speed when printing the top layers, to allow lower layers to cool. The duct is thin and fragile, attach the fan carefully so you don't crush it.