I worried that the screw could possibly back out over time and become loose in the wing rib so I replaced the screws with nylon hex head bolts, and glued a scrap of wood against one of the flats to keep it from backing out.

I thought about using steel bolts, with nylon nuts, so there would be no chance of stripping the bolt; but decided to stick with nylon. You could “gun drill” a steel bolt with a 1/8 (or slightly bigger) hole to eliminate some of the extra weight.

If you go the blind nut route, which I think is a really good idea, be sure they are glued in securely or they will fall out and force you to cut into the wing.