There are many posts on here about roof leaks. I have seen posts where the water leaked in at the front of the trailer, traveled 30 feet along the roof to come out at the sky light in the bathroom in the rear. My unit is currently in the FR factory shop having the siding repaired for just such a leak. As for tracking down the breach allowing the water to come in, I suggest that you closely inspect all joints for cracks, holes, or voids. Many find that slideouts are a good source of leaks.
You can get a "pressure test" done at a dealer and that will enable the tech to locate the leak source. I have seen a post on here that someone has instructions on how to do your own pressure test.