Alternatively you could put "feet" on the corners of the glass just enough to raise it 1/4" above the tank. That will cut down on the strain of the cord and allow plenty of air circulation from the surrounding air.
Feet material suggestions: some foam squares/strips/rectangles from meat trays glued together, sharpie marker to color them. Hardware store cork, furniture feet, stack of magnet strips if your tank rim is metal or even felt. Make sure your glue is dry and cured before introducing into the tank area. Stack of custom-cut magnet strips would be my choice.