I have the Hopkins wifi one, where you supply your own "device" as the monitor. Posting about it here I learned that there is a distance problem with wifi that might be cured by having one of those booster gizmos in the front of the trailer for the camera in the back. That booster in the front would be closer to the dash of the truck. AFAIK a typical trailer-truck situation is too far without a wifi booster in the front of the trailer.
The Hopkins works for me ok in the class C and truck camper with their shorter distances. I use an old iPad mini as the monitor, held on the rear view mirror with elastic bands and plugged into the cig lighter as its charger. Makes driving the MH or TC much easier, but you still have to use your side mirrors as usual.
The other big thing is that my wifi version has a time delay in the picture, caused by "processing time". This makes a car that looks like it is starting to pass you be at your side window at the same time! Takes a bit of getting used to. also with mine, a tailgater looks like he is well back, so you can't believe the way it looks for how far back they are.
It was posted that the "wired" cameras do not have this time delay, and of course you need to somehow run a wire for this job from trailer to truck and through the truck to the dash for the monitor. Lots of people do that, so it can't be too hard.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.