A NATO trailer will want the hitch as high as possible, it's probably why all Defenders get the reinforced holes in the rear crossmember, you rarely see a MOD Defender with a tow-hitch right?
Plus if you want a 50mm ball and NATO you need them to be a long way apart, 50mm ball should be about 16v inches from the floor, the NATOD wants to just miss the bottom of your back door
Otherwise put them both on removeable saddle slike in your picture, but a Sankey will sit really nose down.