Davit,
I think I saw something like what you meant. What is the name of the gadget?
I'm unimpressed with what the Hvac people did 19 years ago to install ductwork. They took out a crossbeam, and that should have been compensated for. Now that I've taken some courses in house framing, and building, I have better than 20/20 vision. Unfortunately, it's too late to do much.
Today I was reminded to measure twice, and cut once. I tried blocking another space in the basement cold room, and the template I cut was too large for the duct.
No problem, since I have more cardboard. And I love reusing!
But I'm going to measure twice.