If you carry the gun into and out of the house, it will condense moisture in the barrel, and its possible that the powder will be fouled. The secret is to leave it outside in some secure place when you are inside getting warm again!
If you have already taken it inside, I think you should pull this load, or fire it off, and then clean the barrel again. Use alcohol to flush out any remaining water, and let the alcohol evaporate.That will dry the barrel, powder chamber, and flash channel. Then put a new load i the barrel.
To provide a better vapor barrier, put a piece of plastic wrap under the PRB before driving both down the barrel. That will seal the powder from any moisture coming down the barrel. Use a good lube on the patch that won't dry out.
Then when you remove the cap when you get home, put a piece of plastic wrap over the nipple and lower the hammer down on top of it. That will seal the nipple so moisture can't get into the powder from that end.
Maintained this way, you should be able to go 2 weeks without ever worrying if the powder will ignite. I leave the plastic wrap on the nipple, and put the cap over it. When the cap fires, it easily burns through the plastic wrap and ignites the powder.
You don't have to spend money for Saran Wrap or some other wrap. If you buy bread, every loaf comes in a plastic bag. They work just fine for a seal on any percussion rifle. put the rest of the bag over your stockings, to keep the liners in your boots dry. That will keep your feet warmer, too. :thumbsup: