See if you have a rental store near you that will rent an ozone generator. These are used to remove odors from buildings after floods, fires, dead bodies, etc.
Besides removing the odors it will kill any existing mold and mildew.
Once you have things back to neutral, and you make sure that you have no dead critters in the basement compartments or in the bottoms of any of the cabinets, then you can worry about ventilation. Pull out all drawers to make sure that no food dropped behind them.
I live on a lake and less than a mile from the Gulf and all I do to ventilate my coach when it is in storage is to open the top power vent covers. I have the vent covers that will allow the vents to be open even during rain. I do not run any fans and allow the normal convection currents of hot air rising to circulate the air.
I've been doing this for many many years and have not had any mold or mildew or odor problems.
I think you will find the odor to be from some food left in a cabinet or a dead critter in a hidden area.