IMHO if you want to do the job once and right, put in a Bohlman concrete water and install it exactly per the instructions.  I use two 3 ft long 12" dia heat tube sections, the top one insulated, the bottom one just std 12" plastic culvert.  I put a Miraco foot valve in on all waterers so I can shut off the water if its not used some winter and then I do not need to keep the electricity to it.