I recently installed a 4 camera wired system from Amazon since the 3 camera system on our Class A had seen better days. Since I installed it without interaction from the ignition system and powered directly from our battery bank I can have it on whenever I choose. Amazon had a plethora of wired and wireless cameras for virtually every type of vehicle or scenario, ours came with a remote and 9" screen to toggle or view all cameras simultaneously.
Went with wired since we have a 40' rig and didn't want to have signal issues although some of the higher-end wireless models have a transmitter extender that helps to alleviate this situation. Our system also records videos from all cameras at the same time and can accept SD memory cards for added storage, I have never had a need or desire to view any of the footage. Indeed it would be great security, have not been compelled thus far to utilize it as such.