Search - Hound heater dog house furnace.
I be afraid of chewing with the pad's
I use a small electric heater with thermo. kinda ducted to back of 2 crates.(heater is away from anything remotely flammable)Crates are also on styrofoam ins. as above.I only use this at night though otherwise there outside in kennels with dog houses stuffed with cedar shaving's

looking into hound Hound heater for outside kennel look's pretty good.

Keep us posted on what you come up with