I made my first sleeping bag using two Army surplus sleeping bag covers (once ubiquitous and cheap) filled with feathers from a couple of pillows. The warmth to weight ratio was not high, but the warmth to cost ratio was. I put the covers one inside the other and sewed them together in tubes. I then opened a couple of old pillows and transferred the feathers using my mother's vacuum cleaner. For me it worked fine. For my mom not so much. The shop vac idea should work fine, but as others have suggested, I think the tent idea is a good one as well.