I don't know if there is a definitive problem, that's why I said concern. I realize that carbon bicycles are clear-coated with UV resistant(?) paint but I'm not sure how the grit-rain-sun exposure on an extended tour will effect it. I have heard that even a small cut/abrasion in the clear-coat can allow the fibers to soak in water and compromise the frame's integrity. I don't know the truthiness of this but it sounds logical.

Although steel frames are vulnerable to water, rust is not a fast process, with respect to compromising a frame's integrity. Plus steel is easily re-painted, stripped to the metal itself, not just touched up. I've re-painted my 40-yo steel bicycle several times, and it's still my daily ride.

As an aside, re-painting a bicycle a new color is nice and can be aesthetically pleasing. Don't know if carbon bikes could handle it.