Use a RTD or a thermocouple. A mechanical (bimetal) thermostat will also
work (see oven supplies etc). The last method is the least recommended
unless you use several thermostats and a tapped heater.

I once made a thermostated plate out of a cooker plate with 5 taps. I used
a double thermostat (washing machine) to switch 500W to 100W at 40C and
100W off at 55C. It keeps 0.5l of chemical solution at 55 +/- 0.5C after
30 minutes heatup. The total thermal mass is about 0.5l solution + 1kg
iron (heater cooking plate).

You don't really need rocket science for these things. Just adjusting the
power with a dimmer at constant air flow will probably be enough. A high
temperature thermometer can be bought for pennies in a hardware store
(cooking thermostat for oven). Most DMMs have a plug for K type
thermocouple which should cover your temperature range.

good luck,

Peter

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