I was interested to see the orange heater pad. I had a look on eBay but stumbled across motor cycle handle bar heaters which are flexible and laminated and run on nominally 12 volts.
I had an idea that the number of LEDs you are using would run quite warm. I am considering getting some of these LED strips which are relatively inexpensive apart from the cost of some kind of heatsink arrangement :
https://neonica.eu/led-strip-neonica-growy.html