I got the same sun roof except in the 20"x32" was super easy to install. Fined where you want it to sit, find center, lay out template that comes with it, trace with a sharpe (red, black or silver depending on body color) Drill a hole in the roof somewhere inside the line(step drill works good for this), Use a jigsaw with a fine tooth metal saw (Plasma,Tin Snips, die grinder) and carefully cut out the center section. Put the top ring onto the truck then lift up slightly and use window urathain not the crap tape they give you, put the bottom ring on loosely with the screws, let the top ring down into the urathain then start tightening the screws from the center out in an X pattern. Once the Urathain is dry can go around the edge and cut the excess off. Inside you put the screw strip on and you're done.

If you have a roof liner after you use the template on the roof drill a small hole in each corner, from inside use a straight edge and cut the liner between the holes. The roof liner gets trapped between the lower ring and the upper ring top keep it in place.

This is what mine looks like looking up
Headliner.jpg