I dont think that obfuscation is in any way useful to protect you there. Indeed, it is more likely to frustrate youafter you forget how you obfuscated. Just rely on keeping the whole thing secret, which it needs to be anyway.
The whole thing should be a secret and stored safely. Buried in your backyard, a fake drain pipe, or even in your usual safe. You should also have multiple backups in different locations, and possibly another one in a location different than where you live or work.
Using steel makes it fireproof (or rather fire resistant), but not rust proof. You'd need stainless or other metals or alloys for that.
People regularly keep books and other important documents very safe, so doing steel washers and nuts and bolts are just fun things.
I once used "plausible deniability" in the form of my laptop dual booting. The default boot mode required no password and boots to either freshly installed Linux Mint or some Windows 98 crap (which I'll probably upgrade to Windows 10) and some downloaded free videos, my resume, and assorted bank files and bills. In order to boot to the second partition I needed to enter a password within 30 seconds, otherwise it would boot the first partition.
These days, I just get lazy and don't bother. Anything I need to keep secret I simply do not bring with me on my laptop and access it remotely, securely, from my home server.
I travel with kids, we always skip the lines, even during this pandemic.
To note, I have been intending to buy a hardware wallet, either a trezor or a ledger, yet feel hesistant, after all these years. And one could say I know enough about bitcoin and the possibility of being hacked or losing them and have been around awhile. I'm doing fine without one so far. Yes, I still want to get one, just haven't pulled the trigger.