I made a heated cookie tin last year and used it this past winter.
It's just a Christmas cookie tin with a lamp cord with double candlebra bulbs? …Maybe they are appliance bulbs inside. (Total hillbilly but it works) I need to make more.
Disclaimer..... I do cover it with a thin rubber mat similar to a drawer liner and secure water to prevent spilling and it's tied in to a GFCI outlet and I don't use it in the coop.
Hard part is getting the cookie tins out of the house before wife notices. She's found me a few at garage sales and thrift stores or will occasionally throw me one of her many she retires from use.