Hello,
I'm embarking upon my first DIY tarp project using the BlackCat tarp instructions here http://www.teamgunnparker.com/blackc...k_Cat_Tarp.htm

The main problem I'm going (haven't started yet though it's pinned) to have is the flat-felled seam of course.

Is it absolutely necessary to fold the "upper" fabric over and under, then sew it? I'm wondering if having a raw edge here is detrimental to structure or sealing.

Also, what about doing the seam without folding it over, a double- stitch, then sewing grosgrain all the way along the tarp, on the underneath side? That would cover up and strengthen the ridgeline while keeping the seam's rough edge concealed underneath.

This all is since I just tried a flat-felled seam on a remnant and found it very difficult to keep it folded under for the duration of the seam.

Some folks have been mentioning using rubber cement, silicon sealant, etc to glue down the folded-edge to sew. Anyone 100% certain of the effectiveness of these methods? Or partially?

Thanks for the hints guys. I'm going to grab some beer for this one.