Why do you want all that complex technology? Just put gaps at the top and bottom of the cabinet, the heat created by the router and what not will create a natural convection inside the cabinet hot air will go out of the top gap and cool room air will come in from the bottom. My cabinet is only slightly smaller than yours, I have a router a wireless access point and a cable modem in it, all of them get scorching hot (not exactly state of the art) The air temperature inside the cabinet isn't even 10 degrees F over ambient. Just for reference the actual metal case of my router is 120 F under normal conditions. The only thing ventilating my cabinet is a slot above and bellow the front door that are each 25mm long and about 3mm high.