Strength with 3 oz should be adequate. Doubling on the inside under the cockpit sounds like a good idea to me to. If you are concerned about abrasion at the bottom of the bow, you might also want to double up there too - just 3 or 4 inches wide. Pygmy calls for an abrasion tape strip the whole length of their kayaks.

: The boat is a single seat kayak of my own design, 5.05m by .55m, and has no
: flat sections anywhere aside from a little V well behind the cockpit.
: Outside of that, it is all compound curves.

: I weigh a bit under 80 kg dry.

: It seems that 6 oz cloth is pretty commonly used, but that seems pretty
: heavy/overkill to me?