I've seen several people on CC refer to the chocolate mousse filling that is simply made from a package of chocolate pudding mix and whipping cream. It seems like something like this would need refrigeration so, those of you who use it, how long do you think it could be left out? Would you use this in a wedding cake (since they normally sit out for several hours)? TIA for the help!

For a chocolate mousse like filling you can use Rich's Bettercream and instant chocolate pudding, this is shelf stable, so you don't have to worry about how long it sets out.

(this isn't a true mousse, but it gets rave reviews!)