I want to try a cake covered in sanding sugar. I plan to adhear the sugar to fondant with piping gel. Just wondering if this can be refrigerated or not. I'm not sure what effect the "sweating" will have on this once taken out of the fridge if it is humid that day. Has anyone done this?

There's no need to put a fondant covered cake in the fridge at all. If it's going to be several days before the cake is eaten, box it, double wrap it and put it in the freezer.

I covered the cake you see in my profile pic with sanding sugar and placed it in the fridge overnight. I didn't have any issues with sweating when I took it out a few hours before I delivered it. It was not a humid day here, but it was a warm October day. HTH

I should have mentioned that I want to use a perishable filling, that's why refrigeration would be needed. Also, I was thinking of using a colored sugar, so I'm worried the color will "run" onto the layer below.