you would need to make it from heat sealable taffeta or oxford for that to work. Silnylon, while waterproof, isn't going to be air tight under any pressure, and neither will the seams even if sealed.
If anyone has expertise with heat sealables, a valved, insulated jacket and pants could be a fun project/ science fair entry. Make it a 1 piece full body suit and you could leave your sleeping pad, bag, and tarp at home. You could roll around in your sleep and be fully cushioned and look similar to the michelin man. Also, it should be bright pink. The mental image of this I got has brightened my day.