Heat tape is used to prevent pipes and other exterior apparatus such as a waterer for poultry from freezing during the winter. Heating tape can be built to any size or shape. You can use resistors to create a heat tape that runs on a 12V battery. The number of resistors and therefore the length of the tape will determine how much power is required and how long the battery will last.
Divide the length you want your heat tape to be by 0.625 to calculate how many resistors to purchase. That will allow you to put a resistor every 5/8-inch (0.625-inch) on your heat tape.
Cut two lengths of 18 AWG copper “Solid hookup wire” and lay them flat on a table 5/8-inch apart.
Position a resistor every 5/8-inch apart across the two wires in a ladder pattern. Make sure to leave 2 inches between the first resistor and the end of the hookup wire on one side.
Heat your soldering iron. Melt solder on top of the two point of contact between the resistor wire and the two hookup wires. Only use one drop and make sure not to put molten solder on the actual resistor.
Cut the excess resistor wire on each side of the ladder.
Cut two lengths of duct tape and one length of rubber door gasket insulation.
Lay the duct tape facing up, put the resistor assembly on top and cover it with the insulation. Cover the assembly with duct tape facing down and press it to stick everything together.
Connect the wire to a continuous 12V power source to turn your heater on.
Polarity of the resistors does not matter when soldering them.
Do not use any other resistors that the one in that article or your heater might fail to heat or catch fire.