: Does anyone have /thoughts/ about how to construct a
: cockpit, including coaming,

find a coaming that you like or mockup the dimensions you like. jigsaw the shape out to the inside dimension, glue(temporary) 1x1foam on top all around the edge, sand the inside edges of yak and foam, layup 6 or 7 ly of 6oz cloth in pcs on the bias, let setup and dig out the foam (if you didn't mask it).

or
others have hot glued in 3/4in tubing or garden hose as a coaming lip form instead of the foam. foam'll get you a more controllable shape.

or
depending on the situation, you could get a little more involved by cutting 2" wider opening all around and making a ditch or partial ditch type recess. look at other yaks first for ideas how will fit your particular shape desired. this would most likely be a 2 step process - ditch 1st, let setup , then foam as before or if yr brave: foam or stubs hot glued on top all around the hole but only sticking in 1 in.,2" wide by 1" foam glued under, shaped then layup. that gives a constant ditch, could easily modify to diff if 2nd layer of 1" foam on the inside to allow more variable ditch upturns.

this is all assuming that the yak is some form of fibreglass not plastic.
and use epoxy as the polyester based resins do not glue/adhere as well, andd epoxy is compatible to the other basic resins, whereas the reverse is not the case.

anyway thoughts.