If you believe the treasure is real then you must accept that the story is real...after all, it's the story that convinced you the treasure is real enough to pursue it.
So what does the story tell us...
1. TB party wanted to make sure their heirs got the treasure in the event they didn't make it back.
2. TB wanted to use an encryption method to protect the secret location of the treasure while they are live yet easy to decode in the event of their death.
3. The "Key" left with the colleague in St Louis did not need the same protection as the cipher numbers; thus, they were kept in an envelope.
4. Being the more important of the two, the encrypted message was put into a locked box.
5. The TB party discussed who could be trusted to guard the box and if necessary, locate and distribute the treasure to the heirs. Ultimately chose Robert Morriss.
6. Robert Morriss, hotel operator, had to be able decode the encrypted message. Based of the three sets of cipher numbers, TB chose a simple book cipher.
There is no reason to change the story or use a different encryption method UNLESS you cannot solve the ciphers.
Let me pose a question to the forum.
If Thomas J. Beale, a Virginian, wrote this story and buried the treasure in Virginia, then why can no one find definitive proof of his existence? People have found similar names, but virtually nothing regarding his specific life, homestead, or family context has ever surfaced.
Secondly, no one has found a shred of physical or documentary evidence in Virginia after 140 years of searching. There are no toll receipts, ferry manifests, or military records that document up to 35 adventurers traversing with 8,000 lbs of precious metals across roughly 1,800 miles of frontier terrain. While some claim the whole thing is a hoax, I posit a third option: the cargo never went to Virginia. It is hard for me to imagine any group that large, traveling that far, with that much high-risk cargo—crossing dangerous lands under Spanish rule, American Rule, and Native American nations completely undetected and incognito, leaving no paper trail other than a couple of letters.
I can believe the underlying truth of the story and the ciphers without accepting the Virginia destination. Just because James B. Ward published a forced, imperfect 'solve' of B2 (where many liberties were taken with the text to make it fit), doesn’t mean the ciphers were ever intended to be book ciphers. That concept is only implied by Ward, who had absolutely nothing to do with the original encryption.
This is not to be argumentative, it’s only my perspective based on the logistical realities of the era. I welcome any dissenting thoughts, I like the discourse.