So you are saying that you have no humid air inside when you close up? and do not have cooler nights to make the humid air condense on the walls?
That is my weather type here in the Ohio River valley... 85 and humid during the day and 65-70 at night, which causes dew to form on everything overnight. Your thin uninsulated roof and walls causes the humid air trapped inside to condense on the roof. You DID mention condensation in your original post, so that is the line I am using to try to explain.
I would buy some Damp Rid at HDepot, several packs of it and put it inside... or look on amazon for those small dehumidifiers that are powered by AC current. The Damp RId will have to be replaced periodically if you are constantly opening and closing the camper... otherwise it will dry the air inside.
a roof leak would pool water on the floor, not distribute it on the walls and roof as you mentioned... or is there a trail of water down the wall pooled on , or soaked on the floor indicating a roof leak?
Just trying to educate you that popup and hybrid trailers do get condensation in humid weather. You are posted on POP-UP forum, and I see only a handful of posts indicating to me that you are relatively new to camping in a popup...
everything I said earlier I stand by, as that is my experience with condensation in my previous popup and my current hybrid...
just trying to help