To make more than one Zoom Tube, you have to make each one reference a different waypoint sequence. The sequence number is specified by the y-length of the Zoom Tube Parameters linedef; a y-length of 0 means sequence 1, a y-length of 1 means sequence 2, and so on.
Each sequence is specified by a chain of Zoom Tube Waypoints, each one with an angle of one degree more than the previous one, starting at a multiple of 256. For example, the first sequence has its first waypoint set to an angle of 0, the second is and angle of 1, and keeps going for as long as you want up to 255. The second sequence has its first waypoint set to an angle of 256, the second is an angle of 257, and keeps going for as long as you want up to 511.
So...yeah, that's how you make more than one Zoom Tube.