I seem to recall someone making one out of metal, sometime ago, as the Jaeger1224 were known to easily become broken, especially at certain points.
Try an internet search, as I think they also provided full instructions, and a guide.
If you can't find that, as it might have gone, check out an old Wheeler Dealers episode, where Edd China had to build a new air conditioning box, for a car, he was working on, out of metal, instead of plastic, as the method should be similar. Don't forget to sound deaden, any construction, you make, to quieten it down.
Edited to add more information.