Well as to the coxial deck fitting,, Not what you need at the roof line. But yes, it might work properly caulked.
As to the Jack.. The Winegard Roadstar "Flying Saucer" is junk, no gain to speak of (though there is a model that appears identical to it that might work, Winegard does not, far as I know, carry it (Radio Shack does) it is a directional flying saucer though)
The Jack, has limited gain compared to the WSinegard Sensar line.
The advantage of the Jack over the Sensar is greater beam width.. Which where I'm currently parked might help. or not.
The advantage of the Winegard over the jack is greater gain (Which means tighter beam width by the way because that is how you create gain)
For me, DISTANCE (Gain = distance) is more important.
In most markets, You find the transmission towers "Clustered" for example.
Top of the highest local mountain.. Studios may be scattered but transmitters are often withen a stones's throw of each other.
Specific Example.. 3 Cities in Michigan
Battle Creek, Kalamazoo, and Grand Rapids.
Transmitters are all close to Gun Lake (in the township, near the lake).
So pointing your antenna in one direction gets 3 major networks and several channels and services (not sure about remaining networks).