Prusa Dual Extruder Dual Fan X Carriage, Fan Duct, Fan Mounts

By designing this I wanted to accomplish a couple of things:

Ability to mount fan(s) in the front of the X carriage instead of the side, allowing for greater X movement.
Use 4 bearings for better stability. I found that the weight of the motor being on the left side of the X carriage tended to tweak that side of the carriage (the front right side where there is no bearing).
Ability to have a fan duct that wraps around two extruders.
Reverse the way the right side belt/tensioner worked so I no longer had to twist the belt.

Updated 7/20/2012

Uploaded repaired STLs and repaired Fan Duct SKP.
Added Fan Mount Cover in case a fan has to be taken out of commission so air does not escape where the fan was mounted.