i have been putting a 2x4 mat under my tent liner and keeps the tent temperatures from dipping too low i put them on controllers so they don't have to be on all the time and doesn't get too warm. actually set all my tents this way, but the seedling tent stays on all the time. it's nice because it offers another level of temperature control, and when it's from the bottom the plants seem to like it better than a room heater.
i have a regular mat but hardly ever use it. i germinate in paper towels in baggies and set them on top of my hot water heater and usually have a good tap root in 2 to 3 days. then straite into a solo cup with half happy frog and half coco.if i use the mat i only put it under half of the germination tray so it dosn't get to got.