I used this Anker 12v USB hub in the rear cargo outlet:
http://a.co/d/8kQCTUZ
It allows me to put the USB ports in the center of the third row for easier access. Keep in mind, however, that 12v plug in the cargo area is powered all the time, even when the vehicle is shut off and locked.
I also used another way to add additional USB ports in the front: A hard-wired connection to the fuse box.
http://a.co/d/iiosaoD
It allows me to add additional accessories very easily and choose a switched fuse that turns on and off. It would be very easily to add one to the fuse box under the cargo floor.