My experience they are all so similar. I buy off ebay cheap.
They work, I have had the same one for probably 8 years.
Bought a newer one for somebody. Bought another and broke it playing around with wires.
For trailer consider just a new system. They make the wireless, but some need a clear line of sight (almost) shot at your screen for really long trailers. This way you just have that trailer cam for when towing.
I am currently playing around with a one-camera system and switching between two cameras - the truck rear and the trailer rear. I'd still use the truck rear for backing up to hitch or to take a peek at front of trailer when towing, but would drive looking at the rear trailer cam. It is just a lot of wire to run, and I have to power the rear camera and remember to not power it when parked.
So, anything on ebay will/should work, they are all so similar.