By couplings, I take it you mean the universal joint couplings - Richard? (Like knurled but even more so.)
It is the core of the Sheerline design, so you wouldn't want to change it anyway, but I think that the design with all those threaded rods is rather old-hat and overkill. German modellers have been rather scathing - what with their bayonet couplings and all!
For anyone building their own WTC, radial O ring seals are the way to go , in my opinion. If you can't find a suitable piece of pipe then look for another one! Even PVC sewer pipe works well. (Not see- through of course, but fine if your sub is not mainly for display.
David