I am doing my sons birthday cake, and will have two tiers, each filled with a different type of mousse (chocolate and vanilla - I cheated and used the Sheriff mousse mixes from the box). These cakes will be crumb coated, then covered with fondant. Usually my cakes have a non-perishable buttercream filling that can rest overnight to prevent bulging before I cover in fondant, but, what would you recommend that I do now because of the mousse filling (they are milk based)? The party is at 11 am so I have no choice but to complete the cake the night before....usually I would leave the finished product on the counter, but in this case it would have to go in the fridge, right?
Thanks!

Yep, has to be refrigerated.

Box cake & wrap box in saran several times. Place in fridge. Take out a few hours before serving, leaving wrapped & boxed. Unbox after it comes to room temp. Perfect.

Rae