Mounting under eave to vinyl siding.
 

I don't want to crush the vinyl siding so what's the best way to mount a j bar to vinyl siding. I know its gotta be simple. Thank you.

Try to find a better place, that's flat.

Not only can you crush it, but it is designed to be able to slide in it's channels, for expansion and contraction. Fasteners, may cause it ti crack, or buckle.