On the one hand, it is important that the recovery boards are safely stowed away. Like everything else in the vehicle. Because anything that is not stowed properly will either be annoying on the tracks due to rattling or can become an unwanted projectile on steep off-road descents or in the event of an emergency stop or even an accident, posing a risk of injury. Especially, please carefully think about everything that goes on the roof rack with regard to your roof load, vehicle height, your center of gravity and ultimately the driving characteristics and safety and weigh up whether it makes sense.
On the other hand, of course we want easy access to the recovery boards. If possible, I recommend a simple attachment where you can get the boards out and back in again quickly. Simply because anything with complicated screws or mechanics can easily break and will be annoying. Wing screws or a knob tend to disappear into the sand and mud forever. Locks get dusty and muddy and then often no longer open. Simple solutions are also easier to repair. I simply have two hooks for my sand ladners on the side of the rig, where I hang them, and two tension locks at the bottom. They still fit in there, even if they are slightly bent after a recovery.