In message , David
writes
I assume that aluminium would be lighter and easier to work with enough
strength for this job.

When we built the boat almost all the stainless steel, aluminium and
copper sheet came from scrapyards. We just climbed onto the piles of
metal and selected suitable sizes and quality.
Of course, I was a bit younger then, and maybe they were less in thrall
to safety.
--
Bill