: ...has anyone here ever built a canvas kayak? If you did, what and when?

I have not done so yet, but "The Aleutian Kayak" by Wolfgang Brinck describes in detail the stretching and sewing of canvas skin on a baidarka. Presumably the same technique would work on other types of kayaks as well. Heat-shrink dacron and nylon are popular also, although more expensive, since they allow some room for error in the sewing department. They are also more rot-resistant, and not subject to the tightening and loosening cycles that canvas undergoes.