Same here found wet spots under overhead mattress.
The water was coming from the weep holes of the windows on the side of the cab over.
I also got to see it first hand during a rain storm. The water was pouring down the side from the window weep hole on one side.
Went outside and could see the water just pouring off the roof down that side. My MH was not perfectly level so the majority of the water on the roof was coming down on 'that' side and the weep hole could not handle it.
I ran my front tire up on just one leveling block on that side and it stopped coming in.
Sooo....
1. The weep holes could be plugged with dust dirt leaves etc. So the water will come in.
or
2. MH not level during a real good down pour of rain.
We must be willing to get rid of the life we've planned,
so as to have the life that is waiting for us.