So when I draped it over the cake, I got the dreaded elephant skin cracks around the edge of the cake despite my best efforts.
A LOT of Googling later, and it turns out you can make a paste of fondant and a small amount of water, and use this like polyfilla or royal icing to fill the cracks. Using a palette knife you smooth it on and scrape it off. Some people call this 'gunge'. I used it to fill the elephant skin cracks in the fondant around the edge of the cake, and in some cracks in the sides where I'd not eased out the folds of fondant very well.
|The smoothed cake edges, no elephant skin!|
I got a kind of smoothed buttercream look which was fine for this cake. Might not be so good if you need a pristine wedding cake for example, but better than nothing.
Sharing in case it helps someone else out!