I've just fitted the rear double USB kit to my 2017 X-trail. Got to have it to keep the kids devices charged on long journeys.
I thought I'd upload the instructions, for anyone who wanted to take a look before they decided to do it. I couldn't see them for the X-Trail anywhere, saw some for the Qashqai.
Some cutting is involved, which didn't bother me, but might be a bit scary for some people. I was going to put USB ports in the back either way, but this kit was much easier as it its plug and play from the 12v socket in the centre console storage bin.
The instructions didn't make much sense to me, but I will add that in Figure 10, it isn't clear that there is a torx head screw to undo, so you can pull the rear panel off with the fans on. You only need to remove this and not the whole lid of the storage bin. To access the screws, there is rectangle piece between the hinges of the lid, that you can just unclip.
It does come with cutting template to line up where you need to cut. I was hoping to fit the ports closer to the top, so the kids don't break it, or any cables when getting in and out, but space is restricted behind the panel, so it does need to be done at the bottom.