@Mark619 I have been using 2 Plant Babies Seed Starter Propagation Heat Mats (10x20 inch) and 1 Apollo Horticulture Seedling Mat (10 x 20 inch). These are basic models...no thermostat or on off switches. Plug them in and they heat. I leave mine plugged in all of the time and only unplug them when we leave the house. My paranoia. I am really happy with both brands. Noticed when looking the past few days that the prices have increased since I purchased mine. Obviously, this is a hobby for me so I don't know what more heavy duty users might use. Love my heat mats. They have done a great job at giving me speedy germination of plumeria seeds. After soaking seeds overnight in H2O2 solution and planting the next morning, I have actually seen germination in 2 days! Happy me! Also using T5 lights.
P.S. When I had a bit of an overflow, I placed some seeds on top of the cable box
not permanently.