Attaching weather vane to ashpalt shingles

Just got a weather vane my wife ordered and want to attach it to the roof of our shed. The mounting bracket is a “universal type” that will adjust to the pitch. Do I just screw this to the top of the roof and silicone the screw heads? Doesn’t sound like the greatest idea. Any help would be appreciated. (she also ordered one for our garage which has cement tiles. Any hints on that? We haven’t installed that roof yet)

Maybe the pic of a lightening Rod will help.
http://www.roofing.com/images/default.jpg

I removed the shingles. Installed the base. Added some geocel and after marking the shingle, cut it and slid it down the unit. I repeated the process with the next 2-3 pieces of cap. Then, I added some geocel and made a washer out of a shingle to cap it off.

All the caulk is out of the weather, and the shingles divert the water and UV rays.