i bought my rv not long ago. it had a backup camera but po told me it didn't work. after done with mechanical things, tires, etc, in last two weekends i dug in and made it work. so you can consider what i am telling you is a first hand experience.
first things first - what are needed:
there are two parts of it: head unit which is mounted to your front panel; and a camera, which is to be mounted on your back wall facing toad. There is an rca cable sending video from camera to head unit, and power sources to camera as well as to head unit. In most configs, it is required that a signal line telling camera to start sending image be in place (only vehicle is in reverse gear).
second: what are good -
my head unit from po was a good one, alpine iva-w505. it has 7" lcd with radio, dvd player and gps. it works great now with sharp image but i wouldn't recommend it because it is not user friendly on menu, and each time when power is disconnected you will need to go through a routine to set it right; otherwise you will only hear audio but no video. a simpler and good one seems to be pioneer in the market now but you will still need to bypass the video restriction by installing a relay (the default is when driving it only allows audio maybe by law. i bypassed it so that even I am driving the dvd can still play - safety harzard, be careful
the camera is a little tricky too. there are two types of lens in market, ccd and cmos. ccd is much sharper and richer in color, and cost more. if a camera box does not label ccd it's surely a cmos. mine is kenwood ccd-2000, which has a wide viewing angle of 130 degrees (i can see wide and far away, but this model has been discontinued). you may check online/ebay what other new models are out there. recommendations: ccd, wide angle at least 100, with night vision.
if you are a diy type person with experience in electronic or computer hardware, installation should be in no time, knowing you have an older backup camera system in place - that said the cable and power sources are already ready. otherwise, car stereo stores typically charge $70-100 for the installation, not bad.
hope this helps, good luck!!