Almost all motor homes have backup cameras. So do many 5'ers. All of them are mounted quite high, near the marker lights. I'd be inclined to try some temporary locations first. Mounting the camera and getting power to it is a (relatively) simple affair. How are you going to get the signal from the camera to the monitor? I'm assuming that your monitor will be in your truck. Are you going to use a wireless camera? That may be the simplest method.
As for how to, get an 8' step ladder and lean it against the rear of the trailer. Use a box or whatever to put the camera up as high as you can. You can run some temporary power to it because you aren't going to be driving at this time. Play around with the location to find the best spot to show you what's around the rear of your coach. Most camera have a pretty wide lens, so you should find a decent spot fairly easily.
Once you figure out where you would like the camera you can try to figure out how to mount it. My camera has a U-shaped bracket that attaches to the coach and has a hole to run the power leads. You will need a spot about 3" x 6" that is fairly flat. Figure out what's behind the skin there. If the spot is clear, drill the proper holes. If not, look at another location.
The camera doesn't draw a lot of power, but it does draw some. I'd look for something that gets power from your tow vehicle. Check your plug for a terminal that is hot with ignition ON and dead with ignition OFF. That is likely the one that charges the trailer battery. To make sure, get your tow vehicle close enough to hook up the cord. Check the coach battery with a volt meter and note the voltage. Then plug the coach into the tow vehicle, start the engine, and check the voltage again. If it is higher that means that your tow vehicle charges the coach battery, so you can tap into any convenient 12 volt
If your tow vehicle doesn't charge the coach battery you will just have to accept the fact that your coach battery will be down a very small amount more than it was before. No big deal either way.
Driving with your headlights on is a good idea anyway, so tapping into the power for the clearance lights may well be the easiest. A side benefit of that is that if your camera doesn't come on it means that your trailer lights aren't on, either.
Our wireless monitor just plugs into a 12 volt
power port, so your biggest challenge is going to be making the monitor stay put. Ours uses a suction cup so it can attach to the windshield. Remember that your GPS wants to use that same power port, so you may need to get a 12 volt splitter.