For my ham radio, I use a 2m/440 magmount antenna on the roof. I have strong magnets that I put on the inside of the roof panel, under the antenna and that holds it in place. I put tape under the antenna base to protect the roof from being scratched.
It works OK, but really doesn't have a ground plane. I have been thinking about adding a metal plate for that and see if that improves antenna performance.
alan