We bought a new fifth wheel. The first time we pulled it in heavy rain the same thing happened to us. But, we forgot about it because it was a year or two before we drove in heavy rain again. This time we took it to an rv repair shop. The seal along the bottom of the slide was not in place, and I'm sure never had been as evidenced by the previous leak. The shop put in a new one and no more problem with an under the slide leak.
2015 Fleetwood Excursion 33D
2016 Grand Cherokee Limited
Retired Law Enforcement
U.S. Army 1965-1973/RVN 1968-'69
I am the frequent recipient of "Get out of the way old man!"