Does this occur when the slide is in as well? If not I would begin looking at the seals on the inside of the slide. You should have a wipe seal and a bulb seal and if either are not sealing correctly water could be coming inside. Check all around the slide because the water could be entering from the top or opposite side and travelling down by way of the seals or cabling around the area.
US Army (Ret)
2020 Entegra Accolade 37TS
2019 Jeep Grand Cherokee Trailhawk (Toad)
FMCA - F432054