A. Is it possible to sew these guypoints onto sil nylon?
B. It is simply a matter of sewing extra sil nylon to the spot where I want the guy points and then sewing them on robustly?
yes, but use uncoated nylon ... so it won't trap water. sew it to the underside and then stitch the loop on the topside, thru both pieces.
C. Any suggestions re: thread to use/not use?
Use ordinary wt. 100% polyester or nylon. use a size 9 needle
Any tips, tricks or warnings would be appreciated. Thanks.
If the ridgeline is a flat-felled seam (or variant), don't bother with a patch, just sew the guy out to the multi thicknesses of the seam.
For guy outs not on a seam, consider sewing the webbing to a 4 inch silnylon circle and glue that to the panel with silicone glue. Smear a thin layer of glue on the circle and on the place you want the guy out, squeegee off excess, put the pieces together, smooth it out, cover with a small piece of plastic wrap, cover that with a book and pile some weight on.
edit: Thanks to Pan for mentioning sealing any stiched thru seam. For silnylon, I've had good luck using silicon sealer diluted with mineral spirits to about the viscosity of pancake syrup. It brushes on easily, leaves a thin coating and seems to impregnate uncoated fabric. For glued-on guy outs, I leave the weight on for 24 hours, don't know if that is excessive or not. Also, if a glued guy out serves a large panel, I think I'd use a larger patch, like a six inch circle. What is a large panel? not sure. I guess I'd consider a single center guyout on an 8x10 tarp to be serving a large panel but the sides of an ID SilShelterto be small.