This is the rear tow hook location I recommend. One of the two bolt holes already exists on the frame so you just need to drill one more. The washers and nuts are inserted up inside the frame through a slot that is already underneath the frame.
Don't drill all the way through the frame, the washers and nuts need to be inside. Drilling all the way through the frame and placing the nuts on the other side would start a slow inward collapse of the frame & cause a need to continually be retightening them.