What’s happening to this wall?

[CarpeDiem]

The pictures are of the left rear corner of the Rv. Not sure how long it’s looked like this but we just recently noticed it. We had the dehumidifier there for a couple months but moved it after we noted a bit of damage. It seems worse than when we moved the dehumidifier. But it isn’t soft or wet at all and I’ve checked all over the roof/slide/back/under and can’t see any evidence of a leak. Where the arrow is looks and feels like bolts poking through, but I can’t see anything bolted there. The other pic looks like a bad patch job on drywall that someone painted or papered over. BTW we bought it new.

[Morich]

Ouch! Hate to mention it but I think you are seeing the results of water getting in from the outside where it can get confusing because it may come in through a light or possibly the ladder, if I'm reading where you mention correctly. Then once in, it may find something solid like foam sheets and go a distance before it finds another point to get further and further inside.

We have found this around lights on a number of the older junkers we have"salvaged"over the years. The problem with leaks is that they tend to be slow but once inside and out of the sun and wind, the moisture can just set and work on anything wood it finds. One of those is the really thin plywood stuff RV are often lined with and it begins to delaminate and rot to make a really lumpy bumpy surface as it get in where we see it.
The inside is some form of plastic which makes it feel dry!

I might first guess at the taillight as being the suspect but it needs to be pulled and check what's up in that area? If the bulbholder is seriously corroded, water has been there!

[CarpeDiem]

Thanks for that. Too late to take it apart tonight, I’ll post after I pull the taillight off.

[Ray,IN]

Marker lights along the roofline are notorious for leaking water into the walls. What happens is, water leaks into the lens,dirt seals the bottom side, water collects in the lens until it reaches the wiring hole through the cap, then runs along the wiring down into the wall.
What compounds this is using sealant around the clearance light base and eliminating any chance of water draining away. I only seal around the top and sides of clearance lights.

After discovering this I drilled a 1/8" hole in the bottom of each clearance light lens; problem solved..