Need help with leak

I have a 1998 30 foot Classic Limited and it has a leak when it rains. The water shows up next to the sofa on the curb side under the arm and right near the very front of the trailer. It is not a very bad leak, but definitely needs to be fixed. I am thinking that the water might be coming in at the bottom rail where the side of the trailer meets the dark gray part that curves to go under the trailer. There is a trim piece there that I believe is screwed on and then there is a black plastic inset material that covers the screws. I am not certain if this point is above or below the actual floor of the trailer. I am aware that with an Airstream the water could be coming from some point far from where it finally shows up, but any suggestions would be appreciated.



Thanks