The transmission site for WWVB has hundreds of water bottles to insulate the equipment from temperature swings.

https://jila.colorado.edu/news-events/articles/spare-time

That page deserves its own submission. The juxtaposition in running four atomic clocks with a UPS consisting of "two car batteries, a power supply, a trickle charger (to keep the batteries continuously charged), and two car headlights (for discharging the batteries)" and a thermal mass consisting of water bottles is crazy

I do this same trick in an insulated utility shed, storing water beneath a desk to prevent overnight freezing within.

Works about as good as a heated rock in your sleeping bag.