: Do I sew on the D-rings for rigging before or after sealing the skin?

Seal the skin first. That way if the D rings need to be replaced you won't have an exposed area of uncoated skin.

While you are sealing the skin, coat both sides of some of the scraps from the fabric you used for the skin. Use these for straps to hold the D rings, and save some for patches.

The holes you'll make by sewing the D rings to the skin will be well above the waterline, and very small. It just takes a drop or two of a seam sealant, varnish-- or whatever you sealed the skin with-- to seal these holes. And if you didn't seal them at all, then you'ld likely have no problems anyhow.

PGJ