If you store your guns in plastic boxes you stand a very good chance of rusting. Plastic doesn't let air circulate and breathe and the gun will rust.
I can't tell you how many guns have been brought into my shop to be refinished that were stored in gun cases, blankets and plastic gun boxes then shoved under the bed until next hunting season and were all rusty when brought out later. Cannons are no different. First, after firing you need to let the guns sit out for a while to get truely dry. A week or so in a dry climate, longer in the humid regions. If you store them away, they should be stored away where air can circulate around them. This is why guns can and will rust in a gun safe. No circulation. Be careful for the same reason with Tampions. Keep the stem short and don't put them right after cleaning. Wait a while until the gun has had a chance to completely dry after a few days.
No matter what you do the the iron hardware on your gun is gonna rust. The Stainless steel stuff is nice but it will corrode also, just not as fast.
Be sure when you build you carriage you use well season dry wood, especially is you use the oaks. The tannic acids in oak will go after iron.
Periodically you need to take you carriage apart and check for rust an corrosion. If rust gets started in the through bolt not only can it weaken the bolt, but rust swells and can split and weaken your wood. It's not good to learn this while firing.
Just a little bit of advice based on my experience.
