Fan Duct for Prusa Mendel Longboat

I have a Prusa Mendel Longboat. It has an aluminium X carriage and J head nozzle hot end. I couldn’t find a duct that would fit so here’s my version to fit the Longboat.
If accommodates a 40mm x 40mm fan and will clamp on to the edge of the aluminium plate.

I’ve also designed a MOSFET controller to control the fan using a Sanguinololu with Sprinter firmware.
Schematics, instructions and firmware modifications to follow.
UPDATE:
See http://www.thingiverse.com/thing:22202