Precisely what I was looking for. I just need to find a source for the aluminum tubing. Would you let me know where you found it at? It needs 12 mm or about 7/16" I.D. to fit over the "nipple", I had thought about larger tubing to tackle the backpressure problem. On another note, you feel that the hobby knife is tough enough to cut that thin ply on the underside to make the hatch? The stuff is pretty hard, I have broken off the tip on one blade trying to cut some before, I would hate to start this and bugger it up because the blade can't hack it. It would give the thin cut I need, I just don't want the blade to skip out or a bad line. Thanks.