Thoughts:

Glue - I would use either epoxy or polyurathane (Gorilla Glue). Use as
little as possible. Polish the brass and then clean with acetone or IPA to
remove any grease or wax.

I'm assuming these are .30-06 casings? Another way to mount them would be
to knock (press) the primers out of the base and mount them with a #0 screw
through the primer hole.