I have a FREE, old Sierra Designs down mummy bag that you could practice on. It could use a bath. Here is the deal, (1) reimburse me for the postage as soon as you receive it (2) when you are finished with the mods, keep it or give it away here or to a scout. Before you sew on it, shake the bag while holding it vertical to shift the down into the quilt portion. IIRC, holding the bag up to a strong direct light, like the sun, will allow you to see where the down is.