I was wondering why your nails always looked so shiny. Dan does have some pretty feet.
Same thing for me on preparation. Start dry and you will usually stay dry. Don't use traditional black powder, it is hydrophilic, meaning is will readily take in moisture from the environment, more so than Pyrodex, but 777 or Clear Shot are the best for wet weather.
I will also put a strip of tape over the end, but I have had better luck with different types of tape, just a single 1" wide strip of duct tape. I hunt rainy western Washington in November and December for deer. I will usually leave tabs on both side of the barrels making it easy to remove the balance of the remaining tape.
I used cap grippers, made by CVA. These are little orange rubber grippers attached to a "daisy". I attach a daisy to my capper, so I have plenty. The cap grippers make it easier to "un-cap" when you reach your vehicle. The cap grippers also keep the cap "exposed to the elements", same as the nail polish.
The picture below shows what happens when you take care of your rifle and hunt in the rain.
If you look at the barrel you can see a spare "muzzle cover" about 6" from the muzzle. There are also two cap gripper daisy things attached to my capper, in my shirt pocket. If I look soaked, its because I was freakin' soaked.
Start dry, keep it dry on BOTH ends, and develop a routine. One other trick to dry out your barrel, but not foul it up horribly, put a patch on the jag down your barrel, and back it off an inch or so from the breech, then fire your caps. This makes sure that you really dry out that breech.
If I'm worried about the load for any reason, I just fire it off and start from the beginning. You only get one shot.