My wife and I have a 320 rs columbus and the under belly is enclosed with the plastic cardboard. There is about 6 inches of insulation above that but do to numerous water leaks the insulation has been replaced but the plastic is so streched by now that it droops down pretty badly. Thanks 1/243 for the idea of sheet metal. columbus trailers are not well built as far as I'm concerned. Numerous water leaks,electrical problems, furnace problems, floor noises, exhaust fans problems, bad service in chelsea michigan (our dealer). We are not happy campers!