You've found it: The Pro-Grow Propagating Mat (22" x 60") sold with the Pro-Grow GC-1 Thermostat. These are the same heavy duty orange rubber mats that are used by Eliot Coleman and Jason Beam. These are the highest quality propagation heat mats sold and will last for decades. Keep a piece of greenhouse plastic on top and they'll always look like new! Use a piece of foil bubble foil insulation underneath, and all the heat will radiate up to the soil blocks. I've used mine everyday for the last 12 years--no problems, no worries; just steady, even, bottom heat.
Remember: Bottom heat is easiest and best for germinating seeds and rooting cuttings. Holds up to 5 flats easily.
The Propagating Mat is sold with the thermostat and comes with complete instructions. Easy set up, 1-2-3 plug and play!
Pro-Grow Propagationg Mat: 22" x 60". Thick 1/8" rubber.
Cord: 6 Ft. Long
200 Watts @ 120 Volts
Pro-Grow GC-1 Thermostat: Heavy duty construction with all metal enclosure.
Cord: 6 Ft. Long. 30" Copper capillary tube with 6" long copper bulb sensor.
120 Volts, up to 720 Watts, 8 amps.
Thermostat controls up to 2 heat mats (heat mat w/o thermostat sold separately).
And, if you want to control up to 2 heat mats you'll need an outlet adapter, which is a two-plug capable outlet that fits into 1 outlet (2 into 1). Search: "Outlet adapter".