I'm looking for any help, or advice on making my own pair of insulating down pants, similar to Montbell's UL Down Inner Pants.

I was planning on using 1.1 uncoated downproof ripstop from Ed Speer's site, along with his 900 fill down.

Can I just make the pieces, stuff them with down, spread the down evenly, and sew a pattern similar to the Montbell's, in order to keep the down in place, and then stitch it together like normal? Or is that ignorant? I've never worked with down before, so I don't know what to do really. But I've heard the horror stories, so any advice would be much appreciated!