Modified the rear cooling ducts from here and here so that it fits the printer perfectly without hitting anything. I also orientated the fan mounting position the other way compared to the other two models since the fan I used seemed easier to find online. I used a 24V 50x50x15mm blower fan. The results turned out great. I can actually see while its printing as opposed to a front cooling duct and have no clearance issues in the rear. I've attached the SolidWorks (2013) file in case you need to modify it. Please excuse the sloppy modeling techniques. :)Bill of Materials Before Printing The tolerances where the fan mounts on to are pretty tight since there is not much clearance in the back. I also wanted the fan to fit snugly in the duct for efficiency reasons. Although the fan dimensions should be pretty standard, I recommend printing the BLOWER_MOUNT.stl first to test if the fan you have fits. If not, you can adjust accordingly in the SolidWorks file. Printing Must use ABS with this model due to heat considerations being next to the extruder assembly. I printed the inside of the duct and the 2 notches where it mounts onto the printer with supports. You might be able to get away without supports if you already have active cooling. Just note that it is a bit of a pain to remove the supports if you do choose to print with them. Installation Once printed, attach fan and mount behind the extruders. I used some 468MP tape to secure it better since it kind of flops around when your print head is moving fast, but it will be fine without it. Will possibly update mount in future revision. In order to enable the cooling fan you need to connect the fan to the EXTRA_FET port using the 2 pin screwable terminal block. From there you just enable it in your slicer or manually in your gcode.