Mystery leak

I wouldn't disagree with your theory. All I know is, when I close the vents, the leak disappears.

^Sure seems that the effect would be exactly opposite. Like it is for any other vehicle in motion….
Air pressure is lower outside the vehicle due to air speed compared to inside the vehicle.

On ours, I found travelling in the rain with the roof vents open creates a negative pressure which will pull in rain as you travel. Carpet under the slide overlap was always wet when we towed in the rain. No obvious leak anywhere. Drove me crazy until I figured it out.

It only leaks at seams and holes. Don’t have to guess too much. And it’s likely any of the seams on the front cap, clearance lights or side seams nearby.
If the walls and roof don’t show any damage, don’t go exploring.
And floors are easier to fix than walls or roofs.

might have it pressure tested will show where leaks could be.

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I may be able to help, but we need more to give more specific help for your camper.

A few questions to start the discussion.

1. Make, year, and model of the camper so we can look up the floor plan to add context to your wording.

2. Does the camper have fiberglass or corrugated aluminum siding?

3. Are the wall studs, floor joists, and ceiling framing (rafters) made from wood or metal?

4. You stated this

d1h wrote:
You press down on it and its hollow underneath. Its right up against the wall in the front bedroom and probably comes in three or four inches.

Which wall shows the floor damage, the front wall, left side wall, right side wall? Left is the driver's side wall or non-door side wall.

5. Do you know if the walls, ceiling, and floor have fiberglass batt or solid foam block insulation?

6. Do you know what type of roof membrane you have?

7. Any chance of pictures of the inside damage and the outside of the camper showing the outer walls, floor to roof?

Pending the answers to the above, there are ways to investigate where the leak or, more likely, leaks are coming from and how far they have spread before tearing into the camper for repair. I have successfully used a moisture meter (many, many times) to scan the camper and see inside the walls, ceiling, floors, and roof. I'm willing to share how to do this, but we need more information to help better fit your situation.

Hope this helps,

John

Leaks can travel long distances along rails, boards, wiring etc. Look for the obvious then go from there. Also what he said ^^^^

All openings are potential leaks, fan, seams, A/C, windows, lights, etc. Or plumbing.