I did that to mine a few months ago. My wife got me one of the ebay setups for about 150 bucks. It included a camera with night vision and a larger rear-view mirror/display screen that straps on over the existing mirror.

I took the tire cover off the inside of the rear door and removed the spare. If I remember right, there are some threaded nuts on the little rectangular piece inside that you back off, and the piece comes out of the half moon. I used a hole saw and cut a hole I think an inch or inch and a quarter or so, just so happened to be the perfect size for my camera. The camera had a little half inch metal ring that slid around it. I put that ring in the whole and glued it with "Goop" adhesive. Then I slid the camera wires in and threaded the nut on the back of the camera to hold it in place. It works pretty good, pointed at an angle towards the ground behind the VX. It has come in handy when backing up to my trailer or manuvering in my driveway between other vehicles etc.
The display I have is reflective enough to use as a mirror when powered off, although not as reflective as an actual mirror.

The worst thing about it is the wire loom in the rear door opening doesnt have room for the additional wires, or at least for the plugs on the ends. I just popped the gromets out and ran the wires through the openings. It's not weather-tight, but it's good enough for me.