I used a wireliess backup camera from Magellan that mates into their aftermarket (some, not all models) GPS. Had used same on my truck for a backup camera. On the truck it is supplied by the backup light wire, so only broadcasts to the PGS when in reverse. On my class B, I didn't needs it as much but wanted one for my boat trailer to see backing up, so it is mounted by industrial hook and loop tape and wired to the boat battery, hence on all the time. I put a small switch in the add on module that attaches to the GPS, to turn that component on /off as needed so mostly have it showing GPS but can at any time see behind the boat trailer by flipping the switch. I think I'm going to get another camera for the back of the class B so I can see the motorcycle trailer when I'm pulling it and wire it similarly to see it whenever I want, even driving down the road.
That said, the system discussed here looks great for the $$, but I don't want another monitor as my GPS is a 7" size already.
Calgary, AB Canada