Hello, I currently have a duct board trunk from my air handler in the attic to a supply plenum in my kitchen which services the entire first floor. The trunk travels through a closet on the second floor. I need to relocate the plenum on my first floor which means moving the trunk over a foot in the closet space. I plan to do this by transitioning to an offset in the closet. Some photos below of what I plan to have built. Everything below the metal offset will be metal. Question- what is the best way to transition from my duct board trunk to a metal offset? The metal offset will be insulated and drop down through the floor to a new metal plenum. Would inserting the metal offset inside the duct board and then using sheet metal screws with big washers work? The washers would insure the screws don’t go through the duct board. I’m even thinking about using toggle bolts to really connect the two pieces. Thanks!