I got a 40" x 90" 100% polyester mummy style sleeping bag. It works to zip it around the whoopie just past the foot of the hammock and pull it up like an underquilt. It covers past my feet, up to my shoulders, If the whole setup is under a tarp, would it be a good idea to use in frigged winters(-20 maybe -30*F)? I also want to carry a Wool mix blanket in the hammock with me. If this would work for extreme cold, how low would you figure it could go(I'm used to 60 with just a sheet). Is there is anything better for cheap($100 or less) that would work down to -20, -30*F?