They tie into the roof frame directly. And there is a lateral side frame behind that plate that the rail ties into. I'm not so worried about that if I'm honest, the roof racks mounting into those locations are rated at hundreds of lbs load.There are 30 litre and dual 20 litre (40l) fuel/water setups utilizing the rear quarter panel attachment points. That's 30kg and 40kg respectively plus any container weight and bracketry. (Yes, some of the load is shifted to the grab rails.) Have there been failures?
But as beefy as the door hinges are I worry about those being a weak link for highly and constant dynamic load. Maybe over rated but that's what I worry about.