The PDM and PDC stipulate digging a trench around the foundation line of a house and putting in a stone or concrete band of insulation around the periphery of the floor to direct the heat from the earth upward into the house instead of outward. This seems to imply that the house is resting on the bare ground or a concrete slab. Okay, fair enough. What do you do, though, with a mobile home sitting off the ground? If you trap air under the home by skirting it with, say, a band of cinder blocks or bricks -- starting from 18" below ground up to the bottom of the mobile home -- will this be effective or a waste of time? Must the home be sitting on concrete or ground or is there another solution? Many thanks!