I put mine on Thingiverse and included the open scad file. Here you go http://www.thingiverse.com/thing:1830918.
It takes a fan internally to blow air on the underside of the board. I've made two and have them mounted one above the other on the fame as I plan on having the duex5 in it's own enclosure but you could play around with the file. I'm not an OpenScad expert but you should be able to make sense of the file.
HTH
Ian