Can Rust Bullet be used as the rust preventative and the top coat…in other words, can the whole vehicle just be painted with Rust Bullet and left that way as an experiment, without actually painting over it with a top coat color? Has this been done?

Yes, Rust Bullet can be used as a standalone coating. It is UV resistant, so it will not break down in the sun. Keep in Mind that our coatings are no like the premium automotive finishing paints. Youi will not achieve the finish like show cars, or even like what you see on cars today.