I think maybe garvin has a hardmount setup for their roofrack.
Having owned a kargomaster congo cage, I wish now that I'd considered what you're considering. (ton's of weight, lots of vibration, etc from the kongo.)
I'd also look into what they did with the J8, with a very low profile roofrack that connected to a hardened/reinforced set of roof ribs on the inside.
further still definitely look at the bajarack and a set of thule surface mounts. very light, strong rack and you can't beat thule or yakima for quality.