Thinking out side the box,like I do instead of using one of the in roof kits to fit your panels in, how about having a full GRP tray under the panels our roof build up will end up with a full osb sheet under our roof covering, so I was thinking about having a complete fibreglass tray resin bonded onto the osb with any brackets bonded in  an upstand all the way around covered with a flashing to match the metal roof covering    any thoughts.