Bed Rack Universal Aluminium Pickup | BULLFACE - This was £700 new, had it for a few years Adjustable Expedition Load Bed Rack, can go up in height & Width to fit your needs. I have mounted it to my Armadillo Roll Top CoverThe Armadillo Roll Top Cover for Nissan Navara D40 ( Mine is 2015, but fits all D40 models double cab) is missing one plastic bit on the side.
eBay