You will get a different answer from evry painter, but here is mine.

Ask your paint store about the primer, but I bet it's okay to use. Be sure to use metal prep first.

I use only urethane primer, with no problems, and my minimum is a "street and show" quality, on all jobs.

Invest an hour or so, and put a couple extra coats of clear on those bed sides. That way, if you don't like the way the flooring reflects on the sides, you can cut & buff them for a better finish, without having to paint again.