LIke most people, and you, I am concerned about the condition of my barrel where I can't see it, as in between the stock and barrel. I remove the barrel from the stock at least once a year for inspecting, or at least I have until recently. Several years ago, I bought a Swedish Mauser rifle made in 1900. When I took the handguard off the barrel, I found that the prior owner had coated the underside of the handguard, and the barrel channel in the wood stock with something that resembles water pump grease. The metal on the barrel protected by the handguard looked terrific, and had the original blue on it, while, the portion of the barrel that is exposed beyong the handguard is missing all its blue, has nicks, and scratches from hard use by the home guard. The stock has scorch marks on the bottom from where it was left on the mantle of a fireplace and someone got too big a fire going in the fireplace at least once! The stock is Walnut, and is now 100 years old and very stable. I have no intention of changing it, scars and all. It shoots very well, BTW>
That gun has taught me a lesson on gun care. I live in central Illinois, where it can get a little warm in the summertime. But nothing like how hot it is in Florida or Texas where I have relatives. I am not so sure how hot you can get this water pump grease without it melting- I have some research to do- but I know we now have synthetic lubes made of silicon, that suffer a wide range of temperatures without melting, or hardening. If your gun maker did not seal the barrel channel and lock mortises with stock finish when he finished your gun, you may want to consider either using a stock finish to seal them yourself, coat the channels with several layers of wax( I use the wax on my finished gun stocks before going out into wet weather with it, just as added insurance), or fill that channel with a good lube that will not harden or melt under the typical weather conditions where you live, before putting the barrel back in the stock. The excess will squeeze out, and you can wipe it off and forget it. THEN, there is no need to take the barrel out of the stock to check for rust, just as Swampman is advocating. I do believe that your lock should be removed and cleaned frequently, and reoiled after an inspection. Crud does have a way of finding a route behind the lockplate and into the workings. Stocks do breathe some, and the movement can cause a temporary gap between the lock and the side of the barrel. Flintlocks are a little better about this, as the pan, and its structure protect the action by redirecting the dirt up and away from the lock, while a percussion lock spits it down and into the lock, in my experience. Fences not withstanding, I also find more crud in the locks on my percussion guns than I have on my fintlocks. I learned that the first time I cleaned the gun after converting my .50 from percussion to flint!