you always need something under fondant, whether bc or some kind of jam, to get the fondant to stick to the cake. most people do a crumb coat of bc, thickness up to yourself. you only really need to refridgerate a cake if it has a perishable filling. some people have problem refidgerating fondant anyway.m planning to make my own marshmellow fondant and was a little confused.. i was going to use a cookie dough filling in between the layers of cake then cover the whole thing with buttercream then lay fondant over the frosted cake.