In our previous coach, I had a 4" parabolic mirror mounted on the dash that let me keep track of any goings on in the coach while underway. Our dog was always tethered, but my wife sometimes moved about to use the bathroom, etc., when traffic was light, so it helped to monitor her location. Our current coach doesn't have enough room on the dash, so I used a smaller 2.5" mirror this time, but it still works as well. Both were found in auto parts stores.
I got a mirror out of the baby/infant section at Wal Mart -it's meant for the car so you can monitor a baby in the back. It has several mounting options and is parabolic. I clipped mine to the overhang area in front of the cockpit so I can see the dog and watch for any "mishaps" like stuff falling, cabinets coming open, etc.
I wouldn't mind one myself just to see what banged open back there I was even thinking of using the Garmin 770 wireless rear view camera option and mounting it somewhere behind me. Then I could switch to camera and take a quick look.