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One could use a simple ON/OFF* temperature controller with a 12V high current relay with the often supplied thermocouple situated on or near the glass to control the heater to be at or slightly above the ambient temperature to ensure that the glass temperature does not reach the dew point temperature for the conditions.
One thing of interest to the above in terms of determining a crude temperature set point: If you heat the glass to the ambient temperature it will always be above or equal to the dewpoint temperature. (It will be equal to the dewpoint point temperature when the air's relative humidity is 100%.) You could use less power if you finessed the air's condition, but that would require some assumptions and/or at least one other air parameter, such as its relative humidity, wet bulb temperature, etc... and using say a psychrometric chart for air to determine its condition.
*If you want it more sophisticated you could also go for a PID type controller with PWM type output.
A bit of a project.
Best
JA
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