Did not want to leave my last post on this thead alone, given the results of the following:
Tried the McNett urethane sealant and found that it would not securely bond the back of a velcro pile square to the PU coated side of a scrap of 4 oz. Spectra Gridstop (peeled off fairly easily)(let it cure in a warm place). Then tried Elmer's ProBond urethane glue, and could not pull the velcro off. Have had good success with the Elmer's repairing the soles of Keen mids, and glueing velcro pile patches in them to improve fit.
Tried both the above sealants with silnylon strips on the Gridstop, and they both peeled off easily. Got me to wondering about how to seal the edge of a silnylon pole sleeve (chosen for strength and elasticity) with a Cuben canopy; so tried Permatex autoglass sealant on the Cuben, and voila', it worked even better than seamgrip, and being a silicone adhesive, adheres well to silnylon.
So tried bonding a strip of silnylon to 2K Cuben with the Permatex. It adhered well enough to pull (with only moderate effort) the mylar coat off the Cuben, exposing the fiber threads.
The posts on this site about the effectiveness of bonding Cuben with Hysol are very convincing, but does the Hysol penetrate into the Cuben threads to keep the mylar from delaminating as above under stress? If not, then stitching may be required for secure seams, with the bonding material being used to both reinforce and seal the seams.
At least I've found a good way to seal silnylon to Cuben seams, but am now concerned about just how rugged the Cuben really is. An even greater concern is about how well the mylar covering will hold up to repeated creasing of the Cuben material from folding and stuffing over time. As of now, I plan to go ahead and use it for the front half of a tent canopy, so time may tell.