Propane regulator - timed shut off

I have seen modenr gas ranges with that type of oven timer.

You may be able to get the control part and adapt it. They usually require a thermocuple in the flame. If the flame stops, the valve shuts off.

A 12 timer and a solenoid valve would do on a car battery. Make it normally closed and the battery holds it open until the timer shuts the volts off.

That is fail safe.

think about a furnace for parts to adapt. there is a thermostat that can be controlled by a timer. your local heater guy throws away systems when the heat exchanger goes bad. you dont have a problem with carbon monoxide.

for electric, my dad uses a hot plate with wood chips. travel trailers have heat systems that might be about the right size for gas.

The only concern I have is leaving a gas burner unattended is a potential disaster. You need to monitor the flame to make sure the gas is burnt and not just being vented into the chamber and turning it into a bomb.

I would look at using a boiler or furnace controller as they have everything you need built in. Just make sure that the way you build it is fail safe, i.e. it shuts down in the event of a fault or failure.

the refrigeration industry has a electricaly opperated control device called a sortie valve for multiplex comercial refrigeration systems like at grocery stores. It may or may not work.