On our new unit it was leaking under the metal from in which the glass door slide. Had water on the floor and down below in the cargo compartment. Some clear silicone caulk fixed it. Your problem may be different but don't assume anything is water tight until you find the source.
2016 Ram 3500HD 6.7L CTD 4x4 CCSB
2017 CC 34RL2 Hathaway Edition
Andersen Ultimate 5th Wheel Hitch
Nights Camped: 2017=61
Nights Camped: 2018=25
Nights Camped: 2019=12 | Booked=6