I made a vented enclosure for the Maslow CNC Router arduino and motor shield. This is built around a 80mm computer fan. You will also need:

6x M3x5mm nylon standoffs
6x M3x5mm nylon Philips head screws
6x M3 Hex nuts
3x JST 6 pin connectors (to be honest, the only connectors that fit were 5s lipo balance ports meant for RC aircraft)

You will need to solder up extenders to connect the internal ports to the outside of the case. Simply solder a male to female cable approx. 75mm long, and glue it in place in the opening in the back of the case.

The zip file also contains IGES, STEP, and the original Solidworks files if you want to modify the model.