Dan,

The the tube usually has a little tab (with a hole in it) near the end. As cletis describes, instruction 8 and figure 99 in the 1951 Che Accessory Installation Manual indicate that a screw through that tab is attached to the "dash mat" (the interior firewall cover - near the middle-on-passenger-side, lower down on the mat/cover). You'll see from the diagram/picture that the excess length of the tube is coiled.