Lookin tasty!!
:thumb_up:
If you can find a cooler big enough for your tub, or even a tub big enough, with blankets wrapped around, you can use an aquarium heater. You'll want it pretty insulated. You'd put the aquarium heater in some type of jug, like a soda bottle, jar, etc and fill it with water (aquarium heaters are meant to be run only in water). This way, you'd have a nice heat source that you can regulate. This avoids the issue of the reptile mat applying heat directly.
It's all I use to heat my mushie babies!