You really don’t need a frizzen stall on while cased, unless it’s loaded. Anyway your frizzen stalls probably too big. I’ll take a pic of mine when I get to my gun closet.
If you tie a leather thong from your trigger guard to the stall and adjust the length to where you have to tug on the stall to get it to slip over the frizzen it won't come off, I use deer hide which is stretchy. I leave one on my guns if they are loaded and stored for the next hunt shot opportunity that might be months away, I drop the hammer on the stall. If the gun is unloaded, I never put a stall on the frizzen.
I have never had a frizzen rust with the stall on for an extended length of time, but then again, I am a fair-weather hunter and keep my rifles out of the elements.
I hunt with my gun cocked with the stall in place when I am sitting but don't cock the gun when I am walking, for me it is a lot easier and quieter to flip off the stall to take a shot that to cock my gun quietly with very cold fingers.
Mainly I’m using it for protection during transport to and from the range. I pretty much decided that it is too large and needs one side trimmed down to fit.
Who made your stall and of what? Can you post a pic?
I make mine of heavy veg tan on one side (the side against the frizzen face) and stretchy buckskin on the other. It allows for a tight stall to stretch and form fit to the frizzen.
Not the best pics but they are what I had already in my phone's gallery
