Best way to seal/insulate square ductwork?

My furnace is in a 12' X 20' storage room in my basement. Another room in the basement that is a little larger is my Home Theater set up and my computer desk. I have no vents open in my basement, yet the leakage from the ductwork is enough to heat it in the winter and in the summer makes the basement like an icebox. I have often thought that the furnace would be more efficient if I could seal and/or insulate the square and round ductwork in the basement. I have seen the air bubble foil wrap, but wonder if this would be a good solution for the square ductwork? Also, how would this best be accomplished yet still allow for duct cleaning every few years?