In humid conditions moisture may form on cold surfaces like metal ceiling vents depending on how often the entrance door is opened.
If the moisture is coming from around the AC ceiling cover you may have plugged drain holes in the base of the AC unit on the roof. These are the drains that allow the water to run out and down the roof to the ground. If they are plugged which can happen due to debris, dirt or other crud, the water can leak back into the RV.
It's an easy fix. Do a search on YouTube or this forum for tips on cleaning the drin holes.