Well.. it's cold enough where you are ... If I wasn't going below ground level with the floor.. to put it on warmer earth .. I'd definately put my floor on a layer of 2" builders foam... then you can put the sand and pavers right down on it... this would insulate the greenhouse from the frozen ground especially around the edges where the floor of the greenhouse would like to be the same temperature a the ground outside... which is below freezing in the winter.. it would keep it warmer and the pavers would actually store the daytime heat with their solar mass...for use in warming the greenhouse... rather than being a conductor of the heat trying to keep the ground above freezing..
