I have used these type of heat mats for my tortoises for many years and replaced some recently. I place the heat mats above the tortoises’ night shelters inside their greenhouses to keep the temp around 17ºC inside. I may place some bubble wrap loosely above the heat mats to achieve this temperature on cold nights. This method has proved ideal over many years. The tortoises must, of course, NEVER SIT ON TOP OF THE HEAT MATS!
Great Viv, good price easy to collect and quick to assemble.