Thank you for this post. I installed a dual spare wheels carrier, which blocked the rear camera. Upon relocating the camera to the top inside of the rear window, I found out that the velcro fitting of the camera is not great. Now I am thinking of mounting an after market camera bracket and fit the Toyota camera on the outside, bolted underneath of the rear visor.
No issue of dust ingress into the car from anywhere other than the cabin air filter. The fix is to carry a lot of cabin air filter. I carry 2 for replacement at middle and end of dirt track on each long trip.