Kathy, while I appreciate the backup camera I've mounted on my truck - it makes backing much safer and makes hooking up to the trailer much easier, I don't think a backup camera on the trailer is much use.
I mounted one on our trailer and found it didn't really tell me what I needed to know, which is where the trailer is headed when backing. Yes, it does show if the space you're backing into is clear, sort of, but it really doesn't alert you to certain kinds of obstructions like low hanging limbs, some boulders, etc.
So, I've found I do best by getting out of the truck and inspecting the area behind the trailer, then monitoring the "angles" in the truck's mirrors while moving, and getting out frequently to check as backing progresses.
I don't use a backup camera on the trailer.
I should add that backing is a skill that improves with practice. You have to learn when to stop turning the tow vehicle to "point" the trailer and "countersteer" to "follow" the trailer.
- Jack