I also don't want to discourage your experimentation, but perhaps
you have available funds and money isn't an issue- in which case,
a bi-metal sheet is generally supplied in 12 inch (one measurement)
or 6 inch size **s and working with the bond already done seems
like the right way to start.
From here in the UK, the following experience may be of interest.
Many yrs ago one of the products I was making was a deep transparent
ruby red enamel on fine gold.
When gold was $32. dollars an ounce I still needed and wanted a
still lower metal cost.
The need was for a bi metal strip of 1/1000 gold over 9/1000 in.
I talked to Johnson Matthey in Hatton Garden London and they were
happy to make this for me in 3in wide strip by 36in long.
They start with a short block of the 2 metals soldered together,
then roll it out to the final thickness the customer needs.
Bi metal and tri metal sheet has been around a long time, Sheffield
plate was the first commercially available material of this type, as
silver copper silver.
I have a nice example of this in a tray.
Get it made, then turn it into the tube section you need. Time is
hope this helps.