Flashing for night roosting bats

What's the best way to attach long pieces with making it unsightly with fasteners? I'm covering wood. I'm thinking some combination of trim nails and adhesive, but not sure what adhesive would be best. All suggestions welcome.

I do what you have described many times. Just use as many trim nails as needed to hold the flashing piece in position until the adhesive cures. It will stay forever then. I have used silicone and other clear flexing fastening glues for such projects.