I went with the kit from Camera Source. Kinda pricey, but plug and play. It came with a surface mount camera that I mounted on the camper. The camera that came with my kit is not as good as the one in the tailgate, especially in low light. I would consider getting the best camera they offer. Note that my truck does not have the 360 degree camera system. Looks like that kit is even more $$.
I think if you are handy and can get the proper connector, you could make one very cheap.
Let us know what you end up going with.