A/C metal tape or duct clamps are the best way to attach ducting to fans or reflectors. A/C metal tape works good because the glue holds up to being heated & cooled. Duct clamps do not have glue but they have been know to rip the ducting. Some customers use A/C metal tape to attach the duct then use the clamp over the tape, the tape helps stop the duct from ripping when you tighten the clamp.