Thank you for your answer. Unfortunately antifreeze of any sorts is out of the question as the rabbits would inevitably find a way to get in contact with the antifreeze. I would be able to tig-weld a rabbitproof sealed container, but in that case the scope of the project escalates too much for...
Three rabbits will be wintering in a 2m x 2m x 2m wooden hut.
Outside temperature does not go below -30c (-22f)
Planning to put a 50cm by 50cm 1mm thick stainless steel sheet on the floor of the hut (inside off course)
My plan is to heat the sheet with a 50w PTC heater element...