The only thing I can suggest is don't use nylon for your straps. Use polyester; nylon stretches too much and you'll end up scraping the ground with your underquilt possibly losing some down or just stright messing up your uq...And go with what jt said, it's easy! mrmike also has great advice. Also try owfinc (outdoor wilderness fabrics) and magna fabrics for some more diy options.
"We do not go to the green woods and crystal waters to rough it, we go to smooth it."- G. W. Sears
My forum name is Fish<><; I'm in the navy; and I hate sleeping on the ground. If I didn't need ground to walk on or measure resistance to, I think I could happily give it up.