I would be more concerned with the water coming into the upper (or any) fridge vent. Where is that coming from?
Some water may enter as wind blown rain, or towing in rain, but not much. I don't know what others do, but when washing the trailer I am very careful not to spray water onto the fridge vents. It will mostly surely end up inside the trailer, and possibly between the floor covering and plywood subfloor.
As for opening from top vent to bottom, my 25' is wide open inside but don't know about a 23'. I took the extra step of sealing all screws, lines, tape at the bottom of the compartment with sealant to keep any water from draining to the floor.