While I had the headliner off and prior to doing insulation I decided I wanted to wire up a rear view camera. I used a cheap rear-view camera (make sure its rear view so the image is reversed), but purchased one that did not have the backup lines on the screen, I think those are annoying.
I wired it up with a wiring harness similar to this, including a power line in the video wire made it much easier to wire.
To mount the camera I drilled into the top brake light and cut a hole to allow the wire to go into the bottom of the red lens and connected to the harness inside the van. Only concern with this was that it would glow red at night when the brake pedal was pressed, but that was fixed with some electrical tape on the lens.
For the screen, I used a suction cup monitor and found that it worked great for what I wanted. I connected the RCA and the red power line from the rear camera and then attached both the power lines to the D+ 12V line. I did this intentionally so that the camera always runs when the van is on, I really like this method, as opposed to only on when in reverse as I can keep an eye on my bikes or trailer. I also found it very useful when determining when to merge on highways, covers a rear blind spot.
If you don't want it running all the time you could easily add a 12v switch into the D+ line. I will admit it is somewhat bright at night when you hit the brakes.
I found these Zip-Tie Adhesive things really helpful when running wire throughout the van. Then seem to hold pretty well too.