stv,
I can tell you that if you go out to an auto supply and pick up a can of good paste wax w/ carnuba wax and start slathering it all over the barrel, action, screw holes....anywhere you DON'T want the epoxy to stick it will do a great job for you. By the way, don't bother rubbing the wax down, smear it on and let it haze over.......Don't forget to use it on the outside of the stock as well.
Finally, pick up a pound of kid's modeling clay (the stuff in wrapped quarter-pound sticks) and use that as a dam to block the epoxy flow as in just in the stock channel just in front of the action/barrel mount. What kind of epoxy will you be using? Brownell's brand is what most use...... called Acraglass I believe.
Jim