Your deconstruction is coming along nicely. Rotten wood can be discouraging.
So I thought about you and Miss SteemDreem and took a look around. I found something that may be of use, both structurally and to assist float-ability in the rebuild:
Unsinkable aluminum foam:
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Source
The middle example appears to have structural uses across the span you are working with. Especially if bonded to her wrapped with glass cloth and resin.
Do you think this might be helpful ?
oh yeah...I've been looking at box channel aluminium for the motor mount...THIS might work for the internal spars and stringers..
thanks..