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Heated insoles are very useful, I have them in my sailplane when on long and/or high altitude flights. For that they have to be powered by a low-voltage battery, mine has 12V. There should also be a pulsing power supply with the duration of the pulse controlled by a solid state switch. All of that you get in Gerbig insoles that they sell mostly to motorcycle riders (that's where I got mine). A version that you can only use at your desk is useless to me.
Built an 18' stitch and glue kayak from Chesapeake Bay some 15 + years ago and it still looks like new. Used good mahagoni plywood, marine epoxy and expensive clear varnish. These boats should really last forever. Re-varnish from time to time after sanding and they will look like new - mine does.
Wrong, do the scarf joint if you want a quality built boat. Takes more time but it's well worth it. Since a proper boat it covered in glass cloth inside and out, you do get the additional strength that 'sandwich' provides. Also, my kayak was quite torsionally flexible until I added the deck and bulkheads. If you build a narrow canoe you might as well make it a kayak by adding front and back deck covers.