I am making a strawberry shortcake themed cake for my daughters birthday. I plan on covering it with fondant and doing white cake with a fresh strawberry and whipped cream filling. I need to make it the night before, but will the cream filling stay good overnight with out getting all soupy?? What about a filling made with cool whip and fresh berries?
Mary, how cute is your idea! I would refridgerate that cake if you are using real whip cream. Your weather conditions should dictate to you how to handle it.
You will be a bit safer if you use an imitation dairy product such as cool whip, pastry pride, rich's bettercream, etc.
Again, consider the weather conditions for your area.
HTH
Cool Whip isn't shelf stable and requires refrigeration (except for the period the cake is being served).
Please see butternut's response from Kraft on proper Cool Whip storage:
http://cakecentral.com/cake-decorating-ftopict-34791.html
Only Rich's Bettercreme is shelf stable for 5 days at normal room temperature. 
HTH
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