The only heating pads I've found around here have had a 3 hour timer on them before they automagically turn off. REALLY annoying.Get a cheap heat-pad from sunbeam. The inner pad is watertight and can be switched in three level to keep the bebes warm and healthy even in really cold weather. I used those even in the duck house for the Fall Dumped Ducklings of 2020. No fire risk compared to any heat lamp. And ducklings loooooove warmth from below.
I'll keep it in mind though, if I find anything and can actually run power down to the coops. I think they'll be fine, but we shall see. Weather has been crazy everywhere.