What I have found water always comes from above unless your in a boat. It could be traveling inside the wall before seen on the floor (Many times it is). Leaks are not easy to find, it could be from any nearby door, window, corner, hatch,roof, awning. Sorry no easy fix or find. I start with the lowest closest likely cause and spray with water from outside for minutes and go in and see. Wait a day or so and move the spray to the next spot. That's after looking over every inch of the stuff I listed.
2013 24RKSWE (27ft TT) Cougar 1/2 ton series
2013 Ford F350 4x4 CC 6.7 engine, 8 ft bed 3.55 rear end lariat package
Retired from Oregon State Police in 2011 than worked another 9.5 years as a small town traffic cop:
As of 05-2020, I am all done with 39 years total police work. No more uniforms for me.