Tim, What kind of glue do you use? I normally use CA with horn and antler, but that doesn't give me enough open time to get a base plug in place. I normally fit mine in tight and have to heat the horn to get them in. Usually, I don't need a sealer. When I do, I use a little beeswax.
Kind of depends on how much work I want to put into it, hide glue is good but to make a batch takes awhile and it doesn't keep well. Never tried CA, just don't think it would seal as well. If I use any glue it is TitebondIII.
Once I get the horn to just about finished I cut it to length and file/rasp it to to even out the edges. Then it goes in the water and toils for an hour or so, then I put a sizer in and give it a couple wacks with a rubber mallet, it sits and dries a few hours. Then I turn the plug to fit as tight as I can get it. Then finish turning the plug, usually there is a little more work to do on the horn so the base of the horn and plug match up right. A little glue on the plug, press it in and pin it. If the plug fits really well you can skip the glue but on thin horns the pins, especially if they have heads may cause small gaps.
All-in-all to keep it air tight I think glue is a given.
Way more than you asked, got a little carried away.
Tim