I replaced everything for my camera system. Wasn't difficult but can be tricky. My advantage was the camera wasn't enclosed and the rear cap is pretty much open between the interior and exterior walls. Not sure how you're going to get the enclosure open. Drill out the rivets?
To get the power and video wires up to the camera I used a snake to pull them to various points by removing the a tail light, upper corner height light and to the camera. The hardest part was feeding the snake from the 1" camera hole to the 1" height light hole. Under the coach I followed the tail light wires forward along the chassis frame to a hole in the firewall that was behind the dash to connect to the monitor and a 12VDC power source.
A two camera system is pretty easy and low cost while a four camera system, in particular the two side cameras and a multiple input monitor, would be very hard on my budget. I only run one camera and have about a four foot blind spot directly behind the coach but I can see down the road behind me very well. When backing up to an object once if leaves the view of the camera I know I only have a few more feet to work with but usually stop at that point.