KuHL 951

Have you ever actually measured current drain? If your cables and grounds are good then move on to a circuit problem. If it's on an unfused circuit I would suspect your alarm or bad door/hatch/glove box switches that activate the dome lights. 5 batteries in a year sounds like a drain somewhere in the 200-500mA range, especially if it drains overnight on a weak battery. Maybe the insulation on a (+) cable is slightly worn and shorting to the body somewhere. If it was a direct short to ground you would see smoke!