Before you go and do any drilling and cutting, be sure that the camera works for your vehicle.
There was some talk awhile back, about how the cameras were designed for pick-up trucks and vans, and didn't have a strong enough signal to transmit from the rear of a large MH. You know, great for hooking up a trailer, but not for seeing out the back of a 35-40' motorhome.
I'd give it a try with some adapter cables or whatever you need, to put the camera at the back of the MH, and the monitor screen up front where you would use it.
Better to find this out now, rather than later on, after drilling holes!
Now, if the camera you have is made for the RVs, then you should be fine, but I'd still want to check it out first!
If you screw into the wall, just make sure to seal it well (silicone).
I think I remember one person putting their camera right under the top rear running light, and he was able to tie the power cable into the light's wiring. Yes, he had to turn on the lights when he wanted to use the camera, but it was a fairly quick and easy installation.
Good luck:)