Can you put it on a cinder block? Raising it may help.
Off topic, but related: I should be receiveing in the mail today or tomorrow a new heated chicken waterer. I didn't even see a picture of it, but a few BYC members from Iowa mentioned it a few weeks ago, and I've been on the hunt to find it. I have a friend in Iowa that I sent the brand (Farm Innovations) and part number to, and she picked it up last weekend & popped it in the mail Monday. It's supposed to look like a traditional waterer, with domed top, but it's electric/heated with a wire-wrapped cord. Can't wait to see it!