Hi,
I coat most of my barrel channels with a varnish thin layer of Acraglas tinted with Laurel Mtn Forge stain or aniline dye. It does seal the channel but my main reason is it strengthens the thin barrel channel walls greatly. On my guns, those walls get pretty thin. I would guess pentacryl would work as well particularly if you can tint it when needed. With respect to stabilizing the wood, I don't think that is accomplished by sealing the barrel channel because there are so many other avenues of moisture into the wood and none of our traditional finishes are really water proof. The original guns rarely had any finish in the barrel channels and they worked and survived a long time. However, on all of the original 18th century guns I own, the thin sides of the barrel channels are extremely brittle, have been repaired, or are cracking away. Hence, strengthening them should provide some increased level of insurance against breaking.
dave