My opinion about it,
don't see any prof. massive steel cases to prevent RF shielding today. Look at sharias yt-channel, what the industrie is doing.
I mean, this is about voltage references, right? So keep it simple and cost effective. That's for the pcb's too. (€: I don't think, we really want to beat a fluke reference in the first steps... ).
It's more important to pay attention to the basic things and how to measure them correctly. Know, from where the noises really comes from. Read the books, then build a reference, calibrator, or what ever. But not a heavy expensive tank, that doesn't really help much, but tries to solve the problem like under a large pile of sand.
Keep it simple,
have fun,
Using massive block of steel is not only for shielding but to get it hermetic to humidity.
It is simple for me, I have a milling machine, lathe, tig and stick welding and many other mechanical tools, it is easy for me
I just want to test something that I think was never done from volt nuts:
1/ heavy shielding
2/ avoid humidity influence, te massive housing with wall thickness should be about 10 mm, build with 2 parts with gasket (base and cover), silicone isolated wires hermetic sealed, area with silicate gell to remove the humidity after closing the "container", 1 taped hole just above the 10V trimmer but closed with a screw and hermetic gasket. Power supply isolated in a different area shielded from the LTZ1000 pcb.
3/ have a "stable" thermal mass and if needed could easy be heated very accurately.
It will take some months before I can really make some test
And this will cost me just time and maybe 10-20 Euros of metal.
eurofox