Am I correct that the barrel is tensioned on the GK one? I’m looking at the diagram and as far as I can tell the shroud is screwed onto the threaded end of the barrel, and when that nut at the very end is tightened, it tensions the barrel and pushes the shroud against the receiver.
If I ever am at the point of looking for something to fill my time, I might try to design and print an active/sealed shroud. I think it could hold up fine with good thread orientation, especially with the compression from anchoring it to the barrel / receiver. This would also require venting in the nut that attaches it to the barrel - it should be possible to 3-D print a very durable solution, or use one of those screw-in metal threaded inserts or some other solution that screws on the end (I can imagine building something around a hatsan airstripper, for example)