Samuel, beautiful work, do you have a thread here with pics on that tent, I don't want to pull this topic off topic, but I'd love to see a lot of closeups of your work there on the green tent, especially seams and key joints and connections, inside and out. I'm not to the point of being able to make a tent, but I'd love to see what others have done, especially with such an excellent outcome.
Roger, thanks for the input, I'll still try the hemmer presser foot on silnyon to see how it works, slipping, as indicated above, would be what I'd expect though, but if I have to pin to do it well, that's fine, I'll do it, it's just the lazy hacker in me wondering where I can avoid unnecessary work in the end, heh. But necessary stuff, no problem.
Peter, thanks for confirming what struck me as kind of obvious, if you pull at basically one single layer, which is a standard edge of a faux felled seam, not, I realized reading your comments, even two layers, that's totally different than having one seam press down, creating friction of the top layer, onto the next layer, onto the rest of the layer. I know that friction holds are radically stronger than the actual connector alone, thread, screws, etc, from experience, so conceptually that makes total sense. Excellent argument for making true felled seams on especially a tent.
I've had the same experiences with ironing in the folds, but I haven't been able to test durability, ie, if I damaged the silnylon by ironing it, but good point re making sure to only iron the actual fold, I was sloppy in that regard.
One thing I've started to see re myog is that I can do stuff with sewing, by not worrying about speed or efficiency, in terms of stronger seams that take a long time to sew, so it's possible to really exceed standard production techniques in some cases, since my time is free for me, give or take.