You need to cover that from the outside till you can get to it. The water will get between the inner and outer skin and make its way to the floor through the wall and you will never see it. That is probably the single most common place to leak and cause undetected floor damage.
The outside piece should be held down with 4 screws. take it off put a piece of thick plastic down and bolt it back on over it to make a sort term repair till you can do a proper one.
Check all the floors at the walls in that end of the coach and if its wet. Leave cabinets and access pannels off so it is exposed till it can dry out. If its dry out might want to open up the coach to get the humidity down till its dry to prvent mold and mildew forming.
1959 22' Caravanner
1988 R20 454 Suburban.