I also had trouble with lacing my Lug sale. My NE Dory is my first boat, so I wasn't sure if I was using the right line from my kit. But it was the only line that made sense, but it was so large a diameter I had a hard time getting it through the grommets. After my first sail and not being able to get my sail to hang correctly (lots of wrinkles, I couldn't stretch it smooth). I came home and bought some new line locally. Much lesser diameter. Now I can stretch my sail nicely. I'm watching it closely for now, the line I bought came from a big box home improvement store. It is not as nice as the cord provided by CLC, just seems a better fit. It is on its 2nd season and so far no line has failed.

I don't recall my skerry's lugsail kit coming with line for the lashings.  I got a spool of 3mm polyester double braid (brand FSE Robline) at West.  For each corner, do a double purchase lashing, tying an eye in one end and using that end as the standing end, running through the sail and spar with the free end, through the eye and back through.  More purchase for tightening.  Then tie it off on itself with a couple of half hitches and tie a stopper at the end so it's harder to come untied.  Use a hot knife to cut the end really short, and the melted bit helps to keep the stopper in place.  The 3mm (basically 1/8") has more than enough strength and can be looped through the cringles a couple of times.

   Here's a shot showing the corner lashings.  Don't mind the green line.  I was just using it to tie the boom and yard ends together for brailing the sail up against the mast.  The white line is the reefing line, and the blue flecked line is the halyard.

Did something similar on our PMD lug, except we just passed a short length of 1/8 or 3/16 (I forget) through the clew and tack cringles on the foot and the throat and peak cringles on the head, brought both ends of the line through the holes in the ends of boom and yard from opposite sides, both ends tnen back through the cringle from opposite sides, then turned a single overhand knot where the ends crossed inside the cringle to set up and tighten, finishing with a firmly set up reef knot on the outside of the cringle to hold all in place.  Stopper knots on the ends will help get a grip on the braided line.

It's easy to untie to adjust if needed, yet reasonably secure.  We put the tack and the throat closer to the end of the corresponding spars, leaving more length of spar at the clew and the peak, which we thought might look better.  Adjustment is done at the aft ends.

We decided to lace the sail to the spars with a spiral lacing.  Again, we thought it looked better that way.  Also, the tension sort of evens itself out, making it easier to get a good set without puckering.

.....Michael

If it isn't obvious, you do want to use a low-stretch polyester line for this.  Nylon would be too stretchy.

   Anvient thread I know but do any of the above people have pictures of the method theyused for corner lashings and lacings