Pepin, you're right, it wasn't a cable, and I was planning on using some 1/8" Vectran I have on hand. But if I pursue this route, the sailmaker needs to create some curve to the sleeve he'd be adding to the edge. Which is the measurement I'm hoping for.
Tad, it's a little hare to see that pic, but I get the concept. Couldn't the rod be sewn directly into the tramp edge? But I think I'm a bit more comfortable with a system that ignores the C channel entirely.
The sailmaker suggested just putting in a series of grommets down the sides, maybe 5" o.c., and lacing that to a vectran line running from beam to beam. That would eliminate the need to get the curve of the sleeve correct. I assume that if you don't get it correct it'll stress at the corners where the line enters the sleeve, or it'll pucker if there's too much curve.
I'm still undecided....

Dave