Stop in for a cup of coffee

IMO better to duct tape the original. It can't come apart 'cause its one piece of coil.
I was going to buy the gaffers tape but the adhesive is rate to 200F. That's a little too close for this engineer. I like factor of safety when I don't know about something. Got some fire resistant tape that supposed to be good to 200 C. I knew metric system was good for sumptin. LOL.
Polyken Fire Retardant Sealing Duct Tape, Black 268FR | Zoro.com


I see your concern about the high temps, but with getting outside air that will be below 60° to blow through the heater core, chances are the inside air in the ducts will ever get above 150° if that...