Just to mention another possibility, I recently installed a fairly nice wired camera and display with trailer disconnect on my TM. My wife and I are very impressed with it. The night vision is cool too. Actually, the first reason why that one caught my attention is that it has a proper trailer disconnect as part of the kit. The link to where I bought it is:
70CHNV-TRLR kit at www.rvcams.com
The resolution of the camera and display is really nice. It's a 7" color display. We used velcro on the windshield to hang the display in our TV. That way we can easily relocate the display to our other TV or even temporarily relocate the monitor to the interior of the TM if we want to check the camera while we're inside. I'm sooooo glad I have this camera while towing -- it makes such a big difference in safety and knowing if anyone is behind me.
I'm glad I didn't go with anything smaller than a 7" display because it's difficult to see the speed of distant approaching vehicles behind me. That is, the wide angle view of this camera is pretty wide at 130 degrees. So it's really nice to see almost to the bumper while simultaneously seeing above the horizon. But I'd say this is the widest camera lens that would still be acceptable. That's because the size of distant approaching vehicles on the display becomes smaller as you go with a wider angle lens. I can see fine if there's any vehicles within a few car lengths behind me. But beyond that, I really can't tell what speed they're approaching because the image is too small.
Oh - and this camera and display have audio! That's really useful for backing while someone directs me. There's a volume control on this display, so it's all built-in and really easy. Nothing extra or external required to get the sound.
A 2nd port on the display is available for another camera, although we only have 1 camera right now.
I mounted the camera fairly high, but below the running lights and above the top of the rear window covering. The window covering blocks half of the view when it's open and I'm viewing the image from inside the trailer. I mounted it below the running lights because the instructions that came from RVCams recommends it that way so you don't see a red glow in the bottom of the image at night if you were to mount it above those lights.
I routed the cable underneath the rear solar panel and then followed the solar wires back along the legs and underneath along the frame. I don't see any interference from the cable being near the solar wires (especially since that's DC instead of AC wires). I would have found it confusing where to route the cable and how much slack to give the cable near the hinges if I didn't have the solar there as an example.
Overall, my wife and I are really happy with this camera system!
Edit: I used a drill and a Dremel to make the slots a little longer which hold the camera at a slight angle downward. This allowed me to rotate the camera closer to horizontal. It's still pointed below horizontal, but we are much happier with this because distant cars appear larger in the monitor due to perspective or the fish-eye effect of the lens. This means I can get a better idea of how quickly distant cars are approaching. And we don't need to see what's immediately off of the rear bumper. Love it!