Remixed to fit the Anet A2 printer. I tried to use this part first, http://www.thingiverse.com/thing:2057240 but it was sitting too close to the build platform and the sensor holder was on the wrong side. This version is about 3mm higher off the platform and does not have the sensor holder.
The only thing that I had to do post print, other than removing the supports was to drill out the bottom holes for the upper fan as I forgot to put them all the way though the model. Simple fix that anyone should be able to manage.
If you use an 8mm proximity sensor, here is the accompanying mount for that http://www.thingiverse.com/thing:2197990
Printed mine using PETG at about 240 C. Only used supports for the upper fan hole.