A fan may not be necessary but I've added one just in case. It is controlled through the GPIO pins that turn on/off a 100mA mini fan glued to the top of the case, after I drilled through a 28mm hole.
Control is through a simple Python file activated by regular CRON requests.
Photo to go here
Python should already be installed but is case it's not...
This will install the latest version of Python
Type in "apt-cache search libpython3" to see which versions of Python are installed.