I just disovered a major breach in my furnace supply air. The installation was done starting with a canvas (I assume) flexible part, then with the rest of the duct on top. It appears as though it was meant to hang from the ceiling, but there is no evidence of any atachment (screws etc.) to keep the next piece above attached.

The feeble attempt to keep the gap closed with foil tape has failed. I suppose the most obvious way to close the gap would be to pinch it closed somehow (very tight space, very little room to move) and put in a bunch of screws to hold the two "lips" together.
Oddly, the gap is just in one corner; in the 3rd pic you can see (I hope) the gap widening as the junction goes away from the camera

Any other ideas?

Pic enclosed show (1) the system, (2) flexible part just above fan (3) next piece above with gap.

Thanks!