I'm a little confused- are you asking about how to run the physical wiring to the camera and the camera itself, or are you asking how to make it engage the camera automatically when putting into reverse?
The former is just a matter of identifying the pathway that the cabling will take and running it, and finding a home for it near the fuel filler. The latter is going to be manufacturer dependent, depending on what they need. Worse, if such a system uses a car's OBD-II port to know when the car is in reverse, it probably won't work with anything but a '96...
'95 Impala SS - bought 2012-06-08 with 6430 miles
Plus a lot of other cars you probably don't care about