Leaky roof, any ideas where it’s coming from ?

Likely the drip rail on that side of the rig. By the time you see it on the inside, it's probably been leaking for awhile to have soaked thru..

So, roof line and probably forward and back from where you see it in the pic..

You could try to "seal" the outside, but damage is probably already done..

Without seeing it, no way to tell for sure, but that's my initial gut feeling by just the pics.

Good luck! Mitch