I have a small [IP66](http://en.wikipedia.org/wiki/IP_Code) [polycarbonate enclosure](http://www.hammondmfg.com/1554FLP.htm) with a [Zirconia-based oxygen sensor](http://en.wikipedia.org/wiki/Oxygen_sensor#Zirconia_sensor) which produces significant amounts of heat (the internal sense element runs at 450C using a 1.5W heating element, sensor surface reaches 85C). The enclosure also contains sensitive analog electronics to read the sensor. The residual heat from the sensor is driving the ambient temperature in the enclosure up past 40C (measured on the outside of the enclosure front panel). The oxygen sensor and another gas sensor are only rated for ambient temperatures of 50C maximum, so I'm worried about keeping those in spec. I'm also concerned about needing temperature compensation for the analog circuits.

How can I remove the excess ambient heat from the enclosure while still maintaining an IP66 rating?