About this 3D model
This fan mount will duct a 40mm fan to your bed. Made for a Prusa and mounts to this x-carriage: http://www.thingiverse.com/thing:23555 One of the images shows the right-side of the bed fan. You can see that the mirrored x-carriage can hold two fans, one for the bed and one for the hot-end. The scad file is attached. Feel free to change and reuse however you want. I'm thinking at some point I may modify it with some mounts for LEDs to make viewing the printing part easier.