While I think it is a novel idea the space that is lost for the rear door application seems like such a waste to me. In my truck with the Pelicans and a drawer system I would be hard pressed to even be able to fit the mounting plate.
On a Disco it would be interesting to see a mounting plate that would cover one of the rear side windows, this by no means is ideal, but could work on a Disco. I would personally carry light quick access items such as space blanket, first aid kit, rain tarp, rain gear, mainly soft goods that would normally take up empty spaces. You will still be carrying things in a non-dust proof container that will shake and shift easily on long hauls.