I agree with Sandia Man. For most of the 12 years that we traveled in our Class A, I had aftermarket rear and side view cameras with separate 7 inch monitors for each view. The larger monitor he describes will work well, especially if you can have it near your line of sight when driving. A 7 inch monitor is too small to use for split screen use.
Having full time side view is very helpful to keep aware of what is in the lane next to you on each side. On my coach, it also helped in heavy rain as the wipers threw large amounts of water on the outside mirror but the side view camera still worked well.
I found the cameras/monitors were not as helpful when driving at night as the oncoming headlights tend to wash out the monitor and become too bright for comfort.
Some considerations:
On the rear of the RV, a single camera with tilt & pan or two cameras aimed differently will let you check on the toad and tow bar, and then monitor traffic behind the RV. A camera in the front could be helpful if your monitor also has the dvr function.
If you are willing to run some wires and drill a few small holes, you can have a great system for $200 to $400.
Fred & Vicki
St. Augustine, Florida