These photos show a camera monitor I added , as I didnt like losing my navigation view when I indicated to turn. ( I swapped the original out for a cheap android unit )
The monitor had 2 component leads , yellow monitor , white sound.
The second photo shows the winnebago camera box located behind the radio.
I plugged both my comp leads into this box and wired the monitor using a ignition wire , ground and took the appropriate trigger wire from the radio and voila it works and with sound.
So the stock reversing camera has a working mic