Silicone and keeping the glass up there is probably fine, idk. This plastic E30 one was what I was thinking of. It'd be nice to have an aluminum one for the E53. Even some sort of plastic would be good. I just assume aluminum would be better in 105F direct sunlight through the years. Removing the whole tray from above the roof, etc. An E53 version would need to have a handful of screw mounts for where the headliner attaches, where the tray attaches to the actual roof - aside from whatever seal material would be used to perma-seal it to the roof. I guess it's more trouble than it's worth to do that stuff.