I never tried to spool roll film on in a changing bag. I always felt hat would too constricting. You need more room than a bag affords. Take your stuff to the privy. Block the edges of the door. Then turn out the lights. Wait a few minutes for your eyes to adjust and then block that one little light leak you missed. Then sit on the hopper and spool on your film out in the open. You'll find it both easier and safer for the film re: scratches. And welcome to the dark side.