Try that brooder deal I just did.......................PIPE tape, plugged into a socket & wrapped round & round in a tub or crate & fire bricks on top, then a sack of playsand..............even if the power goes off for 10 hours or so, the sand will retain warmth.
Inddors, it gets to 120 degrees at 1" below the surface, and on the surface it stays about 80, my new hatched babies love it..it is easy to clean after them with a sifter, and non flammable....and the bricks are a great heat sink.........and an added bonus is that the chicks NEED sand & grit, so they are super happy in their sand box !
I want to go in there with them...