One other thing you could have done was installed a thermostat in series to the heater. what that would mean is one of the two leads would have a open/close function when you reach a certain threshold temp. Mcmastercarr might have one. If you had it open at say 40C, you wouldn't have to worry with warping. The heater would just cycle off and on all night. I still think it wouldn't be too warm. I could do a computation. One thing though, how hard does the wind blow? That makes a big heat loss.

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