found this too:

We sometimes make a "proof box" by placing a baking sheet or 9 x 13-inch pan
on top of the stove (we have a gas stove with a pilot light), adding some
hot water, then placing the rising bowl or loaf pans into the water-filled
pan. Cover the whole thing with a proof cover or some other large cover. Put
a thermometer into the water, and replace with hot water when the
temperature drops below 80°F. Another simpler way to keep dough warm is to
simply cover the bowl tightly with plastic wrap, and set it in an unlit gas
oven; the pilot light will keep it warm. If you have an electric oven, turn
it to warm for about 1 minute, turn it off, then place the plastic-covered
bowl in the oven. "Reheat" on warm occasionally; you want the temperature to
remain at about 80°F to 85°F, more or less.