After I got over the stuck patched episode. I treated it like my hooked breech rifles. I removed the barrrel, removed nipple and cleanout screw,squirted mean green down barrel and soaked in a tupperware bowl (luke warm water)standing up for about 2 hours. I then used a 22 caliber brush several time and watched for trash coming out of nipple area. I then used more Mean Green in drum, then patch pumped up and down, looking for more trash, repeat til clean dry and use a good rust preservative. I use alcohol to clean and put a little in drum area and (also use a pipe cleaner on nipple and drum area),lpatch it clean to then load as usual. If you use some type of rust preventive I dont think rust would be a problem.
I also got one of the hose things that replaces the nipple, helps to use warm (not hot will cause flash rusting)water to clean barrel and flush everything out. I turn it upside down and clean barrel with everything flushed and cleaned out. Sure saves a bunch of time using it and not removing barrel. I don't replace nipple till dry and rust preventive is used. I also use antiseize on when reinstalling nipple. IMO your results may be different,just my way to do things.