Think I answered this elsewhere.. Two causes come to mind
#1 on the easy to fix list is the intake air filters it's dripping down through.
CLEAN THEM..  Even if they do not need it, might as well start here.
NOTE, be ready cause if this is the problem when you turn off the A/C or pull a filter it's going to make like Niagra Falls under that thing.
Second (this one is harder) go top side, and remove the top cover, you will most likely need a #2 Phillips.. INSPECT the drip tray and find the drip-lip, the "Spout" were water is SUPPOSED to run off on the roof
On my Carrier Air V's it's on the rear.. If I do not level properly and I'm a bit "Nose Down" the water can drip off the FRONT (inside the RV)
On my Advent Air it's one one side, if I'm tipped to the other side, again water drips off the wrong part (or if I'm nose down)
But #1 is clean the filters.