Going to be frosting a cake using a white chic ganache made with double (heavy) cream and white choc. Will the cake need to be refrigerated because of the cream? It's going to be kept overnight before it's being eaten. Is it unsafe to keep out the fridge? Will keeping it in the fridge ruin the texture of the cake?

if the cake batter had butter in it -- yes the cake texture will be a little tighter when it comes out of the cold even after it gets to room temp -- but no the ganache typically does not need to be kept refrigerated -- although if it is as hot there with the dew point near the caution mark as it is here then the drips might continue on their way -- it's gonna be in the low nineties here and the dewpoint is in the mid 70's -- so the temp will feel near triple digits and even though I am in air conditioning it's plenty warm 

Thanks for the reply. So from a food safety point of view it won't go off then? I'm in England but it's quite hot. Gonna be around 80. I am covering the cake in fondant/sugarpaste icing. I was thinking to do Swiss buttercream inside and then white choc ganache to cover as I was reading that it dries a bit firmer than buttercream so gives a better base for the sugarpaste. Would you agree with that? Although maybe they are referring to regular buttercream and not Swiss. What do you think about using the two types of frosting together

I think the two types of frosting would be fine.  When it is hot, instead of using a ratio of one part heavy cream to three parts white chocolate, as is standard, I use one part heavy cream to four parts of white chocolate, which makes for a firmer ganache.  I do have to warm it slightly in the microwave a time or two while I am frosting the cake to keep it at the right consistency.

don’t think i’ve ever ganached a swiss  buttercream iced cake — I would suggest using a thin layer of American buttercream instead or fridge the cake before ganaching — maybe the warm ganache would be ok on top of room temp swiss meringue but idk — I wouldn’t try it —

I thought she was filling with SMBC.  When I use ganache, I do not put it over buttercream, but I guess it can be done.

oh maybe so -- I guess I got that mixed up