Anyone out there involved in High Altitude Ballooning (HAB) operations might be interested in the space-grade Polyimide Thermofoil flexible heater rig we're using to keep our Vulture 2 spaceplane's rocket motor toasty at altitude.
The propellant doesn't much like the cold, so we need to keep it above -5 degrees C if possible - the minimum guaranteed firing temperature.
The last snap is the heater sealed onto our Ceasaroni 54mm 3G case with heatshrink, and the no-expense-spared $10 aquarium thermostat is to prevent the heater from melting down at altitude, where its mighty 2.24W output can't dissipate.
While the heater is only capable of raising the casing temperature 5 degs C above ambient on the ground, it's a completely different story in the air, or the lack of it.
A recent test flight confirmed the rig works as expected, and will keep the motor nice and warm. There are full details here.