I opted to not attempt to hang a towel rod on the outside wall. Instead, under the cabinet that sits over the toilet, there is plenty of space to hang from that. I will most likely fashion something that screws to the cabinet and then bring down some wood, or wood strips to hang the towel holder. With some nice wood and stain, I can get it looking like it belongs there .... and the wife will be happy. If only I could train her to not use 3 towels when showering