I made first stitch'n'glue kayak about five years ago and I used 300g/sqm cloth on bottom due to scratch resistance. For deck even lightest glass rowing is enough. Just remember to add layer or two inside in seating area to reinforce. As for epoxy on my 4,5m kayak I spent little more than 4kg but it was my first attempt and I was very sloppy with epoxy. Actually it is matter of volume rather than weight and viscosity. Lower viscosity epoxy is much better to cover and seal wood but then You will spent little more this pricey stuff.
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