First up the camera needs to be at least a 90 deg or less, anymore like a 120 deg and you won't see a Kenworth until it is 2 mts from you, I have a cam on the ute and one on the van they feed into a screen which fits over my mirror, since i can't see out the back of the ute the camera takes the mirrors place and I can switch between feeds with touch of a button. If you go for this option get the one that replaces the mirror not the one thats fits over it......they are a pain, too heavy, mounted in the mirror position you don't have any sunlight on screen problems.
Brash Imports have the gear at decent prices and the gear is good.
You don't want one with a GPS combined , updates or failure of one causes problems.
Wireless can be time consuming, not to mention frustrating.