Re: DIY backup camera?
Assuming your cameras are 12v and output standard video signal, you should be able to use them. Commonly you either wire the camera's power lead to the backup lights, or wire it directly to a always hot (switched or unswitched with ignition) power source. In either case, simply run the video feed to whatever monitor you have. Most modern flat-screen stereo headunits have provision for backup cameras.
I ran my video using coax cable I had laying around. I terminated the ends with F connectors and then used F-to-RCA connectors to attach to the camera and the monitor. The coax was really easy to pull through the van cabinets and whatnot, and I only had to drill small holes vs. trying to route a cable that already had RCA plugs on each end.
I wired my camera to the backup lights, but if I had to do it again I'd have the power always on whenever the van is on, so I could toggle my monitor to see out the back even if I'm not in reverse (to check the bikes on the rear rack, etc.). The only issue I see with this is that I guess the camera might burn out faster, since it will always be on and transmitting, vs. only on intermittently when in reverse.