I drove through some snowing areas at Yellowstone recently and it started building up around the camera. Also if you drive on a dirty road it will get covered easily. No big deal to clean it off. I only have one other vehicle with a back-up camera (Ford F150) and the camera is next to the tailgate release - I don't remember ever having to clean that camera other than during a normal trip to the car wash.
I rarely go offroad except for some gravel roads, but I have not had to clean my camera. I do notice that water drops accumulate on the camera during rainy days and can reduce visibility until they dry or are wiped off.
Had to give mine a wipe on several occasions but I’ve got into the habit of looking at it whenever I open the tailgate, especially if I’d noticed it a bit hazy while reversing.
Never had a problem with the front one though, wherever that is.