Brownell's Acraglas has instructions. I did it once but am still blushing about it as I am now more traditional.
You must coat the barrel with release compound or wax, etc. Then you must make some room in the stock for the glass to "go"- it's best to have more than a few thousandths of an inch of glass. So you need to gouge your barrel channel some. You also need room right at the top edge of the forestock for the stuff to "gooze" out. It is also good to have a couple of blowholes for air to go. I'd putty the underlug areas, duct tape the underlugs, etc because if it binds in there, your barrel will never come out again. Same at the breech- fill all of the holes, undercuts, anything that would hang up on the breechplug if the glass got into a crevice.
Mix the bedding compound a little darker than you plan to stain the stock. Darker does not show up against the barrel but lighter does. Make more than you need. Spoon it all along the bottom flat of the inlet and get a fat bead of it there. Flatten the bead out with a wooden paddle etc. Put some extra in at the breech and smear it up against the recoil face. Then install the barrel and use clamps at the tang, muzzle, and 3 places in between to slowly draw the barrel down, evenly, and seat it firmly. Then start cleaning up the mess.
Tell the truth, I'd not do it again unless I had to. I see no advantage and now it rubs me the wrong way. But when we were building back in the day, a friend got a halfstock pre-inletted for a 1" barrel then bought the barrel. That doggone barrel was rough as a cob on the outside and by the time we got it filed down, it was sloppy in the channel. That time it was needed. Would have been a pain to glue in long slivers of wood and we didn't have any to match anyhow.