I think I fixed this issue. Lucky I didn't have to pull the cabinet out, just had to lift the bottom shelf up and the staples flew out
The splitter (hot water line) where the outside shower connects with a clamp was loose. I tighten really hard and the leak stops for now.
I am thinking the leak was there before I bought it and somehow the hot water usage exposed it or it was coincidence? I bought the trailer about 2 months ago and never tested hot water this long.