Plastic totes are usually made out of high density polyethylene and are food safe. For common commercial grades of medium and high-density polyethylene the melting point is typically in the range 120 to 130 °C (248 to 266 °F). The melting point for average, commercial, low-density polyethylene is typically 105 to 115 °C (221 to 239 °F). If you have a durable Rubbermaid or Sterilite tote, there's no need to worry... I've been using mine for a week now with a heat mat at 110°F on the bottom with no problems of degrading, melting, fumes on a 22 gallon with the same heat mat you're using 30-40 gallon zoo-med. All the warning labels say that because they have to put it for the one person that puts it near something unsafe or puts it on some type of plastic that doesn't have a high melting point. Best advantages of using plastic totes over glass tanks for breeding is: Holds humidity better, cheap, doesn't break if dropped. You're good dude.