Oops... Too late to help for this, but I'll share it for future use. I use a "T" nut to attach my rail buttons.

First I'll take a scrap of basswood, or thin ply, and drill a hole to accept the nut. I'll glue a scrap of balsa to the side that mates with the body tube, and shape that to match the inside curve. If the shock cord or parachute can extend down to the area, I use a putty based epoxy to blend the edge to prevent snagging (and bolts that don't protrude beyond the nut). That way I can reliably screw and unscrew the rail button in without fear of weakening the body tube where it's located. It also makes painting a lot easier, as I don't have to mask the button, I can just screw in a bolt, and paint.

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Dreaming of making the rockets I dreamed of as a kid (and then some).

"The Guide says there is an art to flying", said Ford, "or rather a knack."
"The knack lies in learning how to throw yourself at the ground and miss."

Launching is Optional... Landing? That Depends on Trees.