The target temperature is a moving target that varies moment to moment with atmospheric conditions.
Yes, for sure. PID has no issue with a changing set point. It just does a better job of maintaining the setpoint than does bang-bang control like your're using.
Duty cycle is a real concern, and the current design is basically rolling the dice and hoping the heaters never burn out.
I'm betting you will be fine, since the metal conducts heat well and will limit the temperature of the heating element.
I thought all relays were solid state?
Definitely not. It appears the IoT Relay you are using has an electromechanical relay, aka an air-gap relay. This is good/important for safety since it fully disconnects the output when desired. A solid-state relay is a form of transistor and has some leakage voltage even when off. But SSRs can handle applications with high switching rates. For your application, I don't think it's significant, but if you were using a PID controller, you might care.
I'm hoping to walk away and spend my time making things with the equipment.
I completely understand and it's almost for sure the right choice. Thanks again for sharing. I may end up doing something similar down the road.