I have a Kane piglet heat pad, it's red, hard plastic. I got the double size. I would recommend getting the single size unless you want to keep lots of kids in the same pen. LOVE IT. Very warm and economical to use. You can lay it on the floor, it says not to put it on "bedding", I have concrete floors in my barn so it's fine there.
I also use the "radiator" style heaters from the 'marts. I also rig up a tent type cover above my heaters, that helps keep the heat down, where I need it.
I am afraid of starting a fire with the heat lamp style heaters. So, none of my heaters will start a fire if they are turned over or other accident. I protect the cord by running it through a PVC type water pipe.