I could be totally wrong here but I wonder if it isnt condensation somehow causing the drip. I dont know how RV AC units are mounted or sealed but i would investigate condensation before taking things apart very far. I know most, if not all, AC units create condensation especially during humid times (during a rain storm). Perhaps your unit is not removing this properly. It also could be the ducts or vents get super-chilled like the outside of a iced beverage glass. The slow drip seems suspicious to me.
Just a thought.