I don’t have the ability to open Wavelab at the moment, but when you’re in a montage, there is an “effects” drop-down menu as you can see in the picture I posted earlier. Towards the bottom there is an option for “Plug-in Window Handling”. When you select that option you’ll see something about using a shared plug-in window. Engage that, then when you have more than one plug-in on a clip or in the master, all the plugs should share one window and have their own tabs.
Maybe PG or somebody can explain more clearly if you still can’t get it.