Not in a new Defender but in my 2003 110, I've hinged what I call an iternal roof rack which mainly carries two bed rolls but other 'stuff' often finds it's way up there also. Some people use nets in a similar way but by using a bit of excess pool fencing and loading the soft stuff on top, it holds everything nice and firmly in place.
No holes were drilled in the vehicle as I used the existing the existing screws which were securing the rear grab handles to secure the rear support and the front was hinged using two bolts with nyloc nuts in the frame of the (cut down) cargo barrier.
It also eliminates the extra weight of boxes on a roof rack to water/dust proof and it's easy to access.
https://www.aulro.com/app/data/1037/Img_7726.jpg
https://www.aulro.com/app/data/1037/Img_7728.jpg