If your goal is to add exterior surveillance, you'll need multiple cameras, 1 or more DVRs (many are 2 or more channels), and likely a second deep cycle battery to avoid killing the car after a day or three. You could trigger the cameras off either motion or an alarm trigger. Take an output from your alarm, run it to a relay, and then use that to switch your DVR and cameras on and off. The downside to this however is that you'll have a few to several second delay as everything comes online.
If you end up installing something please post some details.