Thanks for the suggestions, all. I did mean a french buttercream, or possibly a meringue one (I prefer the french kind). I didn't think the ingredients would be kind to buttercream, but figured I'd ask. K8 - is your cream cheese filling something you can do ahead and hold? The reason I'm thinking of buttercreams is that while I was experimenting with a yogurt mousse, I'm not sure the schedule for this project will allow me to actually use the mousse (it's set with gelatin, so I'd have to make it when I assemble the cake) - and more importantly, I'm not sure the mousse will survive a 4 hour car drive even if I freeze the whole thing...