I took a picture but can't paste in on this page. Don't know how to!

The copper cap is soldered to a piece of 1/2" copper 3/4" long.

This is then soldered to the 9" piece of 1/2" copper pipe that I flattened out with a hammer about 1" from each end, and then used self tapping screws to secure it to the bottom of plenum.

You could use a piece of flat metal and the 1/2" copper cap screwed to a piece of pipe to hold up the door in the original position. Doesn't have to be copper.
(I'm a plumber so I used copper)

If someone wants to talk on the phone I could call after 9pm Central Time to explain it better. Private message me your number and day you want to talk.