What do the N-SSA and American Artillery Assn say about that as a marriage material for the liner and the outer tube wall? In the olden days, when bp cannons were contemporary pieces, Parrot gun breech bands were married to the tubes by cooling the tube, and heating the outside band, and pressing them to fit. When the 2 materials' temperatures equalized the fit was very tight. The problem with introducing a 3rd substance like epoxy, or cement (as an interior sandwich material, is the dissimilar expansion and shrinkage rates during temperature changes, and different abilities to absorb the shock and pressure of detonation. That said, I know that Steen and Hern both use epoxy and similar materials to keep their liners in place inside the bores. Steen uses steel barrels, which are far stronger than the 19th century iron barrels that were used. What ever you do, be safe, and conservative in your fun.
N-SSA says to be safe, you should use at least 3/8" seamless bore liner (if an iron or bronze tube), and have a 1 full caliber wall thickness at and around the breech. And to keep your loads light. Let's face it, with a projectile, you're unlikely to get a lot of enjoyment out of shooting them in indirect fire. Most cannon shoots are at pretty close range.