I've been trying to find a heater base to use with my plastic 5 gallon waterers. I have two that are vacuum sealed and work great most of the year, but don't have the option of putting a deicer in them during freezing temperatures as it would prevent the vacuum seal. I thought I saw a metal heater base that said it could be used with plastic waterers, but now I can't find it! Any suggestions would be most appreciated.