Look at the drip edge where the siding meets the floor, I had the same type of leak on my slide. The water would run down the side of the slide, hit the drip edge and run into the camper. The problem was the drip edge was installed 1/4" too high.
The fix was to remove the drip edge, remove the caulk, and install eternabond to cover the edge and the flooring, then re-install the drip edge. I went further and removed all the caulk on the slide out and installed eternabond.
Will add pictures later.