Hi Milton...
In my opinion, good towing mirrors are a must, and a real safety tool, but they will not allow you to see things that are very close-in behind the trailer. How close depends on a few things, like the distance from the mirrors to the rear of the trailer, the width of the trailer etc.
Personally, I like being able to see what's right behind me - especially when I'm backing. Having a backup camera with a decently wide field of view lets me see things that are right up close to the bumper. That's just not doable with mirrors.
Of course, it's always a good idea to get out and look yourself before backing, and then to have someone stand there do confirm that the path is clear. I've also found that tree branches near the top of my coach can be hard to see with mirrors or a camera - especially in the dark. It's during those times that it's really nice having someone back there - someone who knows to look up as well as back.
Kev