We did something similar with ours. We dug out a small trench along the perimeter where our skirting was going to be installed. We stapled up a long sheet of poly plastic curtain, and placed 8 foot long foam panels into the trench and fastened their tops to the edge of the mobile. We then hung a 2nd plastic curtain along the outside, and covered the whole shebang with metal roofing panels. After the panels were in place we back filled the trench. Air tight in the winter! For the warmer season we built 2 crawl space doors on opposite ends of the home, with screens to allow for air flow. Come winter those small doors are swapped out with insulated panels again to keep out the cold.