Our 2 camera system was a cheap ebay setup for like $50. The idea was to put them both on the top of the back of the bus, one pointing down at the bumper (our bumper is a 3 ft deck) and one pointing out straight at traffic. Turns out they pretty much do the exact same view, and the cheaper tinier camera was better quality than the other nightvision capable camera, so we just use the one. It gives us a view of the deck and generator and bikes as well as behind the bus and most of the blind spot. Eventually I'll disable the useless other camera and put one on each side of the bus near the driver area facing back down the sides. It really helps for switching lanes and also has the lines on the screen so we can back up within inches of something. It has been one of the best things we've done for ourselves.
My build thread:http://www.skoolie.net/forums/f11/build-thread-for-haulin-oats-and-goats-11237.html#post113500
A gal, a guy, three cats, two dogs, one rabbit, and one goat, traveling the country together.