I don't think there is anything "structural" going on with your camper in the photo. I think that is just black streaking dirt and here's why.
On June 21, 2019, after we had our new Montana 9 months (brand new), we slept in it at home in the drive way. In the morning when we first woke up, I looked out the slide out window in the bed slide and saw streaking on the side of the trailer. I was so interred, I went outside and took photos, because the cool morning air and the warm interior of the camper caused condensation and the condensation had evaporated everywhere except directly over the studs and wall framing (aluminum framing).
I took a bunch of photos, because I figured it would be a good record if I ever needed to figure out exactly where the aluminum wall frame (studs) were, and how they ran. I could see the sweat outline on all 4 sides of the trailer. I went photo crazy!
Now, add "acid rain" dirt in the air, pollen, and just general gunk in the air, over time, and the trailer sides not getting washed, the dirt will begin to get thicker and thicker where it stays wet the longest.
If anything, your camper in the photo's is a demonstration of how thin the wall are, warm inside, cold outside, over time dirt settles again and again, sticking to the spots that stays wet. Thus ... the equivalent of black streaking.
Here's some photos of what mine looked like. What you see is nothing but water condensation, making the outline of the wall framing. Add some dirt, and you'd have some interesting new graphics designs!
I think the reason the back cap of the fifth wheel is not so predominate, is because there is a closet along the back wall and an outside storage area under the closet creating a barrier between the warmth inside the camper and the cool morning air outside the camper.
And for an FYI, this is the only time, that I know of that this happened.
I notice in the photo of the back end, I had not purchased my Furrion Observation camera yet. (No antenna sticking out of the side of the cover where they are installed)