Once, AND NEVER AGAIN, we lost power.
Actually last year.
I still had hot water / stove ( we have gas hot water heater and stove) ) thank goodness.
I filled and re-filled a billion gallon water jugs with hot water and surrounded the enclosures then cover them with blankets

It was ,just, terrible. We were up all night ......for nights on-end!

None of my frogs died - thank goodness.
But..... I did lose a very special ( older) Discus My very large Discus tank was a disaster !

I had some of those heat packs......they did not last long enough.

Finally............we got a generator .... to the rescue.........just in time, I'm sure.

A kerosene heater in an enclosed area is VERY dangerous.