I've managed to successfully mount a pair of Touratech 2-litre bottle racks on to the rear of my Gobi panniers. They only pick up on four holes but are secure and I've tried them off-road with 2-litres of water in the bottles with no problems. My work computer won't allow me to attach photos but pm me with an eMail address if you want any photos. The method was to drill a M4 hole through both skins and use a wood-borer to enlarge the inner hole to 22mm, I then cut a length of 22mm domestic plastic water tube to place between the skins. I used a 50mm M4 dome-headed bolt to join everthing with a 3/8 inch tap-washer between the bottle rack and the outer skin and a 40mm washer on the inner face and nyloc nuts to stop it vibrating undone. I also intend to seal everthing with plummer's silicon to allow the void to be used for storing water if required at a later date.