We've had great success with the wi-fi camera from Swift Hitch - their SH04 model. Since it broadcasts an SSID signal just like your home wi-fi router, you can receive the signal and display it on any number of devices like mobile phones and/or tablets simultaneously. They have an app available to be downloaded that you then install on your phones and tablets. It's friendly to both IOS and Andriod devices.
The camera produces a real time color image that is sharp and clear. It has a magnetic base that also has two holes for using screws for additional mounting security. On our Coachmen Freedom Express 192RBS we have mounted it on the rig's bumper and also recently on a metal platform we installed at the top rear roof seam of our rig. Swift Hitch provides the charging cable to allow you to tap into your running light power. But the camera's own battery has a 5 hour life cycle before needing recharging.
While on the road I grab the camera's wifi signal on either or both of my iPad and iPhone and use the Swift Hitch app on each to access the video. (The vendor does provide some mounting hardware to stick a phone on your dash.)
Range-wise, I have received a healthy, full strength or near full strength wi-fi signal in the cab of our Ridgeline in all travel and weather regimes. So in our case we are talking about a 23'+ length of our couples' camper to the front seat of our truck. Not a huge distance . . . under 40'. But I have tested the signal at much longer distances with the camera mounted in the roof top position - reaching about 100' while I have watched my iPad while walking across our yard away from the rig. The Swift Hitch web site talks about the camera being mounted on top of a full size tractor trailer rig and similar longer distance applications, and I have no reason to doubt the ability of the camera to handle those longer distances than our own application.
We use it all the time. It's really handy if you find yourself in freeway traffic in a major city (happens to us all the time in the Houston area - and was great coming through Chicago this past summer on our way back home from Ohio). And, of course, it is outstanding for back in sites at your campground destination. Still use a pair of walkie talkies to verify everything with the DW, but the camera makes it easy peazy. And it has night time infrared Imaging to allow you to see in dark conditions.
We also use it as an additional security camera at home when it is linked to our home wi-fi network. In that application, you can access the camera's image from anywhere in the world if you have access to the internet. It's a fun and useful device.
2016 Coachmen Freedom Express 192RBS
2018 RAM 1500 Ecodiesel
