I put fondant above the crownboard (if it's needed) encased in a slab of 50mm celotex. I had one colony up at the top apiary this year that needed fondant early on, when I looked in hristmas time they were getting low but the box was full of bees, I knoew we were in for a week of sub zero weather and I had other reasons to be passing near them that week, an ideal time to do a quick switch I thought, with all the bees being tightly clustered,so up I popped, the whole area was a carpet of frost, everything frozen solid (including me) lifted the lid.....carton still full of bees enjoying the last chunk of fondant.