I am trying to make an upside down Top Hat cake  I have 2x vanilla pound cake on the bottom and 3x chocolate cake on top  I DID put a 8" cardboard on the bottom cake but is that enough support ? Or am I going to wake up to a collapsed cake? If you look closely you can see the line where 8" cardboard is....i did smooth it out a little more using Viva method

Why do you think it might collapse?

Because 1. I'm a worrywart and 2. I'm wondering if I needed to support the bottom tier with straws   I'm hoping it will be OKAY as it's not a true double barrel cake  Just put in fridge overnight  Will cover in fondant in the morning 

How tall is it? It looks sturdy from  here! I'd say it really depends how stiff your filling is....now saaay it were a custard, mousse or other soft filling then that's the only time I'd see you possibly running into trouble here. 

Thank you ! It's about 8" high or so  

Just measured to put in fridge and it was 10" with the cake stand  And thankfully, buttercream