What is your camper?
I considered doing it in my previous NorthStar Arrow that had the factory fresh water toilet. This camper has the cassette option available so a retrofit as I investigated it was not going to be all the difficult from what I could see. It does deem kinda pricey to buy the necessary hardware though which was a big deterrent.
If your camper has a cassette option from the factory then I feel that it is more than half the battle... if not you are on your own as to determine its feasibility.
I do not feel it is impossible... a big factor to overcome will be the feasibility of cutting the exterior for the black tank door.