How to store a decorated theme cake overnight?

Maybe... but with that cream cheese icing, it would be safer to keep it refrigerated. Have you considered making your own "cooler"? You could put your cake in a plastic storage bin surrounded by plastic tupperware containers filled with ice. Put the lid on the bin to keep it nice and cool. If you put your homemade cooler in a place where it won't be disturbed, none of the containers should come in contact with the cake. I would probably still put that foil loosely on top- would create even more insulation.