I use an inner cover with a small notch placed in the down side of the cover for ventilation during the winter months, should I close this up or will it cause damp conditions in the hives?
I don't use one myself, but don't think it hurts as long as it's turned down, in regards to the fondant.
I will add that dead-air space and heat retention is something you may want to look at. I like upper entrances, but not all the way to the top. I think the bees use dead-air space and trapped heat and this helps with early brood rearing.