I have repaired a lot of floors and have found that they are almost always easier to repair from the top side. This is especially true of a WH compartment that has a door outside. The floor will be closer to waist level while standing outside.
It is important to remove all wet/soaked particle board, dry the area out and then replace with plywood. If wet particle board is left under the plywood, you will probably trap in moisture and thus mold and mildew. Same goes for walls. If water got behind the sheetrock or paneling, that will also trap mold and mildew.
Today is PERFECT!
All information and advice given is for entertainment and informational purposes only. The person doing the work is solely responsible to insure that their work complies with their local building code and OSHA safety regulations.