I can't imagine that any sort of fairing there would really help aerodynamics all that much.
and in all my research I haven't really come across leak issue from that area. Class C leaks seam to happen at
front windows
side windows
or like mine did leaks at the roof to nosecone transition
For what it's worth, I had several points of failure form what I can tell.
The front corner of the roof membrane wasn't put down well
the top most screw, in the aluminum corner trim with vinyl insert screw cover, had a screw through it form the factory from above the vinyl insert and was barely caulked.
And the worst part was the nosecone skin was short, and was not covered by the corner trim by more than 1mm as it neared the roof....
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