I'm adding to an old post.
I liked subtroll's virtual monitor. I had one side camera, eventually added another side camera/monitor but did not have the monitors in good locations. I recently changed the monitor locations, and I've been very pleased with the results.
Like subtroll, I have a dedicated monitor for the left side, rear view, and right side. The rear view has two camera inputs, one for looking at the toad & tow bar, and another for seeing the traffic behind the motorhome.
The new monitor locations lets me see what's happening around me without taking my eyes off the road. My coach's dash layout was helpful to allow room to do this. Not all motorhomes would have enough real estate left on the dash to support 3 monitors.
Pictures below:


All three monitors are the $39 dollar variety from ebay.
Fred