DD has recently got a pet giant millipede who lives in a plastic tank. I say tank, its actually a very large clear plastic storage box which DD thought would be better for him as it is bigger and way cheaper than any of the actual plastic tanks we saw.
We think he would benefit from a heat mat in winter, the internet isn't very clear on whether millipedes need one or not (possibly skewed as many sites are American so the info could be based on a different climate) but as our house gets cold in winter we think its probably a good idea for him.
What sort of heat mat is okay with a plastic tank? I asked in our local pet shop but they were clueless 
and I don't want to risk using something unsuitable.