I made some out of 1/16" plain aluminum and they've worked fine. They just hold the defrost vent in the proper orientation and a piece of foam rubber cut in a triangle shape keeps the warmed air going in the right spot. As long as you copy the original shape, they'll work fine and won't rattle. In mine the rubber sat on the outside. There are 2 on each side.
Mine has wire clips in the defrost vent location, and there was one rubber wedge (maybe the rest of them straddling the defrost vents evaporated). Makes sense about that.
And Brad's idea about steel banding makes a lot of sense.
Thanks everybody for the ideas.
