Made a drip cake today and was unsure if I should use my Italian Meringue Buttercream by Warren aka Cake Love.  Ended up putting it in the fridge to harden a littleness bit it got rock hard, of course, and now has separated.  Now not sure if I should just use American or French Meringue Buttercream.  Worried about Buttercream melting under the pourable ganache which is why I refrigerated in the first lplace.

Sooo, what is everyone using under their drip ganache?

I use either Italian or American butter cream. The ganache shouldn't be warm. Mine is always room temp and works perfectly. 

When you put the meringue buttercream in the fridge, was it already on the cake? 

Use a thermometer. Meringue buttercream needs to be about 70-75 for you to mess with it (e.g. beat it or ice a cake). If it's too cold, you can warm it up with a heat gun on the side of the mixing bowl or by heating a small amount and adding it back in. If it breaks, it will come back together when it reaches room temp and is beaten. 

Once it's on the cake, you can chill it to prepare for your drip. The optimal temperature for your ganache depends on your particular recipe and when it was made - ganache is about crystallization, not just temp (if it's made with cocoa butter). But maybe start at 85 or so and experiment a little. It shouldn't need to be so hot that it melts your BC too much. 

Here are some we have done. Chocolate SMBC, set in the fridge.  Chocolate ganache warmed slightly to pour on top. :)

I use American Buttercream and it works great. I let my cake chill in the fridge once it has been covered in the final coat of buttercream, then I pour the drip over it. I let the chocolate or ganache cool down before I pour it over the cake. If it is too hot you risk it melting your buttercream or running too fast down your cake onto your board. If it isn't warm enough it won't spread easily. Just play with it! Drip cakes are fun!