Water leaks in 1978 25' rear shower bath

[RichB]

When I took my trailer out of storage, I found water in the back closet. It had been there for a while, as some of the wood dissolved, and much in the very rear had rotted.

I have caulked it with polyeurthene aluminum door and window caulk. That may be part of my problem.

I have reduced the leak, but it is still present, and now is rotting out part of the back closet. I have three questions.

1. How do I figure out where the leak is coming from? It seems to be coming from the lower right bumber area, but it is caulked there, and I cannot see any place that would allow water.

2. How do I determine if my caulking job is solid? I am clearly a novice at this task. Have I used an appropriate caulk?

3. How do I determine how critical the floor damage is? I can't find any descriptions of how the trailer is constructed there. Of course, the first step is to stop the leaks.

Any help would be greatly appreciated.