according to Nissan (what do they know right?) there are three nuts on the interior side...No not n the 2016 so we gently pulled back the overhead and pulled out the four. This is a wide assembly. Looks like a small hole for the wiring and i think the center is recessed into the cab a little bit. The sides are curved aerodynamically and they go out almost to the width of the cab. Looks like they are held down with double sided tape.
i will pull it off this morning and seal that. Then my camper shell will slide right into place. The way it is curved, I think it will be a nice fit with enough clearance to allow independent movement of the cab and bed.
http://www.nicoclub.com/FSM/Titan/2016 Titan/2016 Titan XD/EXL.pdf
http://www.nicoclub.com/FSM/Titan/2016 Titan/2016 Titan XD/INT.pdf