When we had our Class C, this is how it was positioned. This is not my RV, just happened to find it on google images
We never towed anything either. I thought it was great since I was able to drive it backwards anywhere...what the mirrors couldn't see, I could see with the rear camera. I highly recommend it!
The only issues we had was during heavy rain or morning dew, it was difficult to see.
Edit: As far as the angle, I positioned it so the bottom of the camera "barely" saw the rear bumper. I was able back it up leaving a few inches between the rear bumper and the fence. Since it was a wide angle lens, it also helped keep an eye on tailgaters