How NOT to install a satellite antenna...
...or anything on your roof...
Our 2014 Sunstar came with a Winegard Roadtrip In-Motion satellite antenna. I won't bore you with all the troubleshooting I did, but finally, Winegard tech support and I concluded that it was bad. It was set up for Dish, but never worked properly with our new Wally.
So, I found a NIB new model on ebay for $900 with shipping and bought it.
In forensically removing the old antenna, I found some scary things. It had apparently been removed from a previous rig and installed on the Sunstar. None of the parts were out of the box from Winegard. The power cable was spliced on the roof and poorly weatherproofed. The interior grade F connector wasn't properly crimped, and was not weatherproofed at all (green corrosion inside).
Worst of all, the antenna had just been set on the roof and screwed down, with no butyl tape or other sealant between the feet and the roof. So, even though the P.O had liberally gooped the tops of the screws and accessible edges of the feet with household grade latex caulk, water still wept under the feet under the antenna and down the screw shanks. Some of them were corroded to half their original diameter, with no threads left. If we had left the dish on the roof another 4 or 5 years, it could have blown off driving down the highway.
The cable clamps holding the coax and power cable to the roof were screwed down the same way, with the same results.
And, the cable entrance into the receiver cabinet was just a hole in the roof plugged with more caulk. It must have leaked because there were multiple layers of different colors
I installed the new antenna with 1/8" butyl tape between the feet and the roof, used stainless steel screws to screw it down, redid all of the cable clamps the same way, used a Winegard cable entry plate to cover the cables and the hole in the roof (more butyl tape), and then sealed all of the screws and left-over screw holes in the roof with Dicor lap sealant.
The front GPS and SiriusXM antennas were the same way. glued down next to a hole in the roof and sealed with caulk. And that one leaked in our first rain. The antennas are mag mounts and therefore need a ground plane to work properly, so I'm changing that.
If you want to mount a mag mount antenna on a fiberglass roof, mount a painted galvanized plate to the roof (a 4x4 metal junction box cover is better than nothing), and stick the antenna to that.