I will have to say, after watching a lot of videos on YouTube about installing these fans, it was pretty easy. With a little planning on top of the van, I was able to position the vent so that I did not have to deal with any of the raised sheet metal parts of the roof.
I made a template out of the cardboard box that the fan shipped in 13 7/8 x 13 7/8. I eyeballed the position to make sure it was straight and then traced it with a sharpie. Yes, I did check it with a tape and it was right on. Drilled four holes at the corners and then cut out the opening with a jigsaw.
Made sure to cover bottom of the jigsaw base with blue tape as not to scratch the paint. Cleaned the edges up and wiped down the area with a cleaner.
The gasket that comes with the fan is just a white piece of what looks like packing foam. Directions stated to tighten down the screws and wait about 10 minutes before applying caulk. I pre-drilled all the holes and then secured the fan to the roof.
Caulked the screw heads and the flange. I also caulked the inside opening as well Took about an hour from start to finish.