There's no way to stop the lead dust from forming if you're using a steel trap. If you're worried about it getting into the room, you could hook a filtered exhaust fan up to it to control that. Why can't your duct seal trap handle the pellets? I have a duct seal trap that I haven't cleaned out in years. Mine is big enough (10" x 12") that I don't have to shoot at the same spot all the time. I also use multiple bull targets (not always the same ones), that save paper, and spread the impacts around. The pellets just fuse to other pellets in the trap. I expect that when I do clean it out, there may be as much lead in it as duct seal.