I've never seen a changing bag that didn't create dust, and dust always goes to the largest smooth areas of light to medium grey on your negatives.
Get a room with an interior bathroom (no windows) The people will think your strange for asking, but that won't hurt you. Load and unload at night. Use you dark cloth to plug bottom of the door. Just before working, run hot water in the shower, and leave it in bottom of tub. This knocks all? of the dust out of the air, and makes for a pretty clean enviorment. I carry a small handheld vaccum cleaner to dust off all my holders before I go into the bathroom. A blower just moves dust somwhere, so it can fall onto something else.
I carry old film boxes for the minus, and normal negs. I seldom have many plus negs so I just use a divider in one of the other boxes. I always try to have enough holders for a days shoot.