Even with rubber seals around the slide out, whether in or out, water can and does find a way to come in around the seals as they do not form a tight aggressive seal. Your unit (imo) should have a slight tilt to the slide out side for water to flow away from the unit and not into it.
This suggestion is only for water coming in from the out side. I had a water leak in a line in the bath wall and did not know it for months because the tilt of the unit flowed the water under the tub and on to the top of a sewer tank. I parked it one day tilted in the other direction and water flowed under the wall and out to the main floor when the pump was on.
2013 Forest River Salem Hemisphere SBT312QBUD
2001 CrewCab F-250 7.3 PowerStroke Diesel
SuperChip, BTS transmission, 6.0 Trans Cooler