When we had our Cougar, we had the same issue. It was noticed in the spring when the snow was melting of the roof and (well at least here) our springs tend to be a bit wet, shall we say. Anyhow this was indeed on the side with our slideout and windows, but the slide seals and interior bases of the slide was dry. However, the window tracks were soaking wet and so was the carpet down below the window. We checked the weep holes on the outside a bit of blockage, dried out the window tracks, then checked them again in a couple days......only to find them soaking wet again. Turned out from the location where we parked the unit in our yard for the winter, it had a slight uphill slope on the one side. The side we had trouble with was uphill facing (just slightly). So we pulled the unit out from there (tore up the yard something fierce, but whatever, it will grow back), and ensured it was on perfectly level ground, dried the window tracks and the carpet, the rest of the spring was quite wet as well, and we had no further issue. In our case it was that slight up slope on the one side.
It could be you have something similar going on.
2008 F450 & 2012 Arctic Fox 29-5K Silver Fox Edition 5th wheel
Paul & Sheryl