I have a couple of ideas on this. The camera system you buy, may need just a little light inside the boxes for the night-vision to work, so I was thinking when you wire in the power and cable to the cameras(inside the box) , then you may add a little 12 volt dc light (like a tiny "license plate light") inside the box also.

Here's a camera system that might work for you.

http://www.videosystemsbyjim.com/quadhtml.html