I feel very strongly that glass bedding, even on "modern" guns, is NO substitute for proper inletting, and especially on a muzzleloading gun.
Now, I'm not totally opposed to the use of epoxy, everybody has to fix something on a gun every now and then, and sometimes there is just no way to do it otherwise, than to use epoxy.
If you have a gun that has crummy inletting at the breech, sure, bed it (though I would not bed the entire barrel...I think that can cause moisture problems, and rust on the barrel), but I wouldn't start out with the intention of bedding the breech.
I have only found TWO epoxies that I like and think are worthwhile. One is good old J B Weld, which sets up hard and strong, though like most epoxies, doesn't hold onto wood all that well simply because it is too thick and just doesn't soak into the wood enough to get a real good hold on it. The other is Brownell's AcraGlas, which is outstanding stuff. Thin and will soak into the wood and hang on for dear life.
My goal is to never have to use epoxy for anything, but since I'm only close to perfect, and not fully there yet :blah: I still have to glue a piece on here or there...